|1980 Sigma D-10 Anniversary Guitar|
|Manufacturer||Sigma by C. F. Martin & Company|
Guitar maker C.F. Martin & Co., based in Nazareth, Pennsylvania, created a line of inexpensive guitars in 1970 to compete with the increasing number of imported guitars from Japan and elsewhere. The result was Sigma Guitars.
The Sigma line was discontinued by C.F. Martin & Co. in 2007.
In 2011 the German company "AMI Musical Instruments GmbH" purchased the rights to the name and relaunched Sigma Guitars again, this time being produced in China.
Since the U.S. rights to the Sigma brand name and trademark had been allowed to lapse by C.F. Martin & Co. prior to selling the brand to AMI, and had since been picked up by St. Louis Music of Missouri, AMI is not allowed to use the brand name "Sigma" in the U.S. for their current line of guitars. They are distributed and sold in the U.S. as Kindred Guitars. The sole current U.S. distributor is Golden Ark Trading Co, Nazareth, Pa.
Initial construction was in Japan by various manufacturers/factories from 1970 through 1983.
The first Sigmas were typically dreadnought acoustics, although Grand Concert Series (GCS) and classical models were also produced from the early 1970s (1971?) onward. Though other models were produced the most common two throughout the '70's were the Dreadnought models DM-5 (DM12-5) and DR-7 (DR12-7.) D for dreadnought, R for rosewood, M for mahogany and the number denoting the grade of wood, 5, 7, 9, 11, 15. 
Construction moved from Japan from 1970–1983, to Korea from 1984-1994, to Taiwan in 1994 (made in both Korea and Taiwan for the 1994 model year) and finally Indonesia (?–2007). 
In 1980, model designations were added to capitalize on Martin model numbers: the DM-18, DM-19, DR-28, DR-28H, DR-35, DR-41, and DR-45. The were called 'Second Generation' Sigma's by C.F. Martin and featured solid wood top. The "First Generation" DM-5 and DR-7 (laminate wood bodies and tops,) as well as other early models (e.g. GCS-7/CS-7) continued to be built during this time as well.
Pegheads & Logos
Sigma guitars made in Japan from 1970 through 1983.
- The early 70s models (1970 -1975) can be distinguished by a more squared peghead, shaped similarly to that of a "spatula." The logo consisting of a gold decal with the single word in block lettering SIGMA surmounted with the Σ symbol (the Greek letter sigma), in mother of pearl. The sigma symbol is often described as a "sideways M."
- While retaining the same early logo for several more years (c1975/76) the peghead itself began to take on a more tapered shape by 1972.
- Interestingly, on right handed models while playing a Sigma guitar the "sideways M" becomes "right side up" suggesting "M" for Martin.
- By the mid 1970's (c1976) the headstock logo design changed to utilize a gold "Martin style" decal stating "Sigma Guitars" in script with "Est. 1970" underneath in a smaller block font. The headstock shape was also modified, to be more deeply tapered and shaped to resemble their Martin brethren.
- As is traditional with classical instruments, Sigma classical guitars do not have the headstock logo, and one must rely on the inner label for identification.
Labels and Brands
Sigma's made in Japan from 1970 through 1979 used a paper label to identify the model and serial number of the instrument. The model and serial numbers were usually stamped on in ink, but some are known to have been hand-penned. This is especially true of unusual, special (sample/prototype models) and/or low production number models (e.g: DT-30.)
- The 'Black and White' label: The earliest examples had a plain black on white inner paper label showing the model and serial numbers. These will show a 4-digit serial number.
- The 'Gold' label: The next generation of labels are transition labels that are white w/Sigma and three horizontal lines in gold ink, the Greek sigma in black and printed black text (Made for C.F. Martin & Co, etc.) everywhere else. These will have a 4, 5 or 8 digit (7*0XXXXX) serial number stamped or hand written on them. More about the 8-digit serial numbers later.
- The 'Purple' label (c1972 onward): These are again white labels that had gold & black lettering but this time with a border, often pinkish-brown or violet in color. The Σ symbol now also in this same pink/purple color. All other text was printed in black ink, or stamped on in ink by the manufacturer (model and serial numbers.) 5-digit, or 8-digit serial numbers.
- The Back Brace Brand: From 1980 through 1983, the end of Japanese production, the center back brace is pressure stamped, or "branded" in a football shape stating Sigma Guitars/Made in Japan/For/C.F. Martin & Co. prefixed by the serial number assigned to the instrument and followed by an ink stamp of the model number. (e.g. L-R as seen through the sound hole: Serial number, "Brand," Model number.) The serial numbers on these instruments were often preceded by a letter; e.g. S0XXXXX.
- Early Korean made guitars show this same brand, only stating Made in Korea in place of Made in Japan.
- During later Korean made years (c1990,) Sigma transitioned back to paper labels and they stayed that way until the end of production in Indonesia in 2007. (Further detailed information is required here.)
Under the best of circumstances, Sigma serial numbers can only provide an indicator of the year in which a particular model was built. This may be due to them being built in several Japanese factories at the same time with no coordination or tracking in the numbering system.  However, while some models lasted the entire run from 1970 through 1983, others did not and were only offered for a limited number of years. Other physical indicators or attributes, such as finish, trim, tuners, etc, can help determine the approximate construction date of a particular example, but almost never exactly.
- For example, serial numbers on the earliest DR-7's began using 4 digit numbers on through 5 digit numbers, with some early 70's models (c1972-c1975) along the way with the unusual 7*0XXXXX, 8-digit system. (See below for that explanation.)
- One Original Sigma DR-7 owner stated "I have an old Sigma DR-7 Guitar....s/n 6860. I bought it new in 1970." Furthermore, DR-7's with a four digit ink stamped label serial number, a zero fret and an adjustable bridge saddle strongly suggests a very early ('70-'71) build date.
- Some early 70s Sigma guitar serial numbers (c1972-1975) began with 7X0 suggesting the 197X build date (e.g. 750XXXXX possibly equates to a build year 1975.) These were eight digits long, the third digit always a place-holding 0, while all others by then were still only five digit serial numbers further adding to the confusion. It is widely assumed by owners and Sigma historians that this is correct, though C.F. Martin cannot, or will not confirm this.
- "Sigma-Martin USA" guitars built in 1981 and 1982 only, had specifically assigned serial numbers ranging from 900,001 to 902,908 (2,907 in total.) These serial numbers are documented by C.F. Martin & Co. and to this day remain the only Sigma related serial numbers that are publicly available.
- These "N" instruments of which there were only two models ever produced, the DR-28N & DR-35N partially assembled in Japan and were imported to Nazareth ("N") and the Martin guitar factory as "kits". There they were completed and finished alongside the regular Martin production line. Bridges and tuners may have been installed, as well final sanding and finishing before strings were installed and a final set-up was done. Because more than 30% of the work was completed within the borders of the United States, Martin was legally allowed to designate them as Made in U.S.A. 
- Serial numbers for Sigma guitars built in South Korea, Taiwan and Indonesia are perhaps even more meaningless, though again some seem to indicate the year of manufacture (e.g. 81XXXXXX.) Since we know these instruments were manufactured from 1984 through 2007 in these three countries, it is safe to assume that a serial number beginning with 81XXXXXX (which I have personally seen) were not produced in 1981 and that these serial number 'indicators' are not to be trusted.
- In 1980 the paper labels were discontinued and the inner back brace was "branded." Later Korean production show a resurgence in the paper label system for model and serial number, sometimes along with the brand. These had an even fancier border. 
- re: My own first Sigma, a DM12-5, which I purchased new in mid-1977 (I still have the receipt) had this second gen "Martin style" decal logo. It being a smaller, local store, the instrument may have been sitting there for a while before I acquired it. While I cannot be absolutely certain of the year it was manufactured, it was certainly by, or prior to 1977.
- High end models such as the D-10 Anniversary model have the "Second Generation" logo inlaid in the headstock using mother of pearl, as do many of the later Korean produced instruments.
- Some guitars made later in Taiwan and Indonesia have a different headstock shape and decal: The shape is more squared off at the top corners, while the decal states, "Sigma Guitars" on top with a miniature version of the "C.F. Martin & Co." logo underneath. Some of these guitars also had the "Est 1970" instead of the C.F. Martin & Co.," using a slightly different block font that is both fatter & wider than the original 2nd series instruments. The paper labels for model/serial number identification had also changed again, this time with a fancy border and the word "Sigma" or "Sigma Guitars" printed in gold ink.
- The issue of whether or not Sigma guitars are solid wood or "plywood"laminate wood has been a source of controversy and confusion for many years now. All known Sigma guitars have laminated sides and back wood. This is no longer in question. This is understandable since the Martin customer service department now responds to individual inquiries stating "all" Sigma's had laminate back/sides, while Sigma catalogs from the early 70s list the back/side wood as "Matched." (edit: "Matched" does not mean solid, but is a careful marketing nomenclature for laminate to confuse potential buyers.)
In the 70's Sigma produced a line of guitars with model numbers starting with 52S, e.g., 52SDM-5, 52SDR-7 and 52SGCS-7. While it was thought at one time that these were somehow 'special' and had solid tops, based on current research and scholarship, an emerging school of thought dismisses this notion, as no primary or secondary documentation exists to substantaite this notion and documentation that no solid top Sigma under numerical model designation 8 exists. Further, tests conducted on the 52S models clearly show that they are, in fact, wholly laminate bodies. The rule of thumb applies here: Most Sigma guitars under the numerical model number 8 are wholly laminate bodies. 
- The answer to the question "Are Sigma guitars solid wood or laminate?" is best answered with: it is safest to assume that all Sigma's have laminated sides and back woods. The top wood is another matter entirely. Many had laminated tops. Models designated "Second Generation" or in the "Marquis" series models had solid spruce tops and the cost reflected this upgrade as well, around $100 in USD more.
Other Sigma instruments included mandolins, banjos, acoustic and electric Bass guitar basses and solidbody and Semi-acoustic guitar|hollow body electric guitars. Some solid body electric guitars were made by Tokai Guitars Company, LTD.
After Sigma musical instruments were built in Japan, Korea, Taiwan and finally Indonesia, they were sent to Martin & Co. in Nazareth, Pennsylvania to be inspected and adjusted by Martin personnel before going to an authorized retail store for sale to the public. These inspections and adjustments were made in the "old" Martin building on North St. (1859,) then known as the Import house.
The DR-28 was manufactured in Japan, Korea and Taiwan while the SDR-28 and the SDR-28H appear to have been manufactured in Korea and Taiwan only, starting in early 1984. The DR-28/SDR-28 have a solid Spruce top with laminated Rosewood sides and back.
The DR-28 and SDR-28 and SDR-28H are clones to the original Martin D-28 and HD-28 guitars and are high quality instruments.
- It has been suggested that these Second Generation branded instruments were the precursor, or pilot program for what has now become C.F. Martins own in-house, less expensive, "LX" series of laminated wood guitars 
Martin discontinued the Sigma line in 2007, and in 2011 the German company "AMI Musical Instruments GmbH" (AMI) acquired the rights to the brand from C.F. Martin and relaunched Sigma Guitars worldwide. However, after a year or more of AMI energetically reviving the Sigma brand with an extensive 75 model range of acoustic and electric/acoustic instruments, all closely following Martin designs, it was discovered that C.F.Martin had, inexplicably allowed their rights to the Sigma brand name in US territories to lapse –
- (United States law states that: In contrast to copyright or patent law, trademark protection does not have a set duration or definite expiration date. Trademark rights … expire when the owner stops using the mark in commerce ……. federal trademark registrations expire ten years after the registration date, unless renewed within one year prior to the expiration – See: http://en.wikipedia.org/wiki/United_States_trademark_law#Limits_on_trademark_law) –)
Further more, the US rights to the lapsed ‘Sigma’ brand name had expired prior to C.F. Martins intended sale of the brand to AMI and has been revived by St Louis Music of Missouri, who currently offer a four model range of Martin clones, all sporting a ‘block style’ Sigma logo similar to that which appeared on the very early Japanese output marketed by C.F. Martin. As a result of this confused situation it has been necessary for AMI, and their US distributor Golden Ark Trading, Inc, to change the name under which their guitars are sold in USA to ‘Kindred Guitars’. This brand name appears to the left of the Sigma banner on the “http://www.sigma-guitars.com” website
Basic Characteristics of Made in Japan Sigma Guitars
From 1970 to approximately 1975:
- Adjustable bridge on all dreadnought (except DJ-7, Dreadnought/Jacaranda) and GCS (Grand Concert Series) models, but this too is an inconsistency as not all had the adjustable bridge.
- Peghead is a unique "spatula" shape that differs from the traditional Martin peghead design in that it is more square than tapered, as the later 2nd Gen models were. These 'spatula' shaped headstocks only lasted the first few years before taking on a more tapered appearance and shape.
- Original peghead logo Sigma with Greek symbol Σ above,
- Adjustable truss rod through peghead through 1979.
- The first year 1970 DR-7 has a zero fret as well as some of the 12-strings did to approximately 1973, or 1975 (DM12-5.)
- Early examples often have adjustable height bridge saddles as well. These were discontinued earlier in the 7 series 6-string models than the 5-series, 12-strings and other "lesser" models. Adjustable saddles are considered less desirable as they did not come in full contact with the bridge and soundboard, and therefore did not offer full sound or the best quality.
From approximately 1976 to 1983:
- Nonadjustable bridge, often showing a pair of pearloid screw covers.
- Martin style peghead (tapered)
- "Martin style" gold decal peghead logo stating "Sigma Guitars" in script with "Est. 1970" underneath in a smaller block font.
- In the early 1980s, some special instruments, such as the D-10 Anniversary, and DR-28H models, have an inset pearl/pearloid logo. The "Est. 1970" is underlined in these cases.
- Adjustable truss bar through peghead from 1970 through 1979. Truss rod adjustments were accessed through the sound hole from 1980 forward.
- From approximately 1980 through 1983, and in later Korean made instruments with few exceptions, stamps, or "brands" were embossed into the back brace wood instead of using a paper label. Labels would return later during the Korean years and continue through final production in Taiwan and Indonesia.
- There were only a few types of tuning machines used during these years. All were basic and inexpensive. There are three different shapes of the buttons on these tuners. Oval in the early models, a more square shape ala' Schaller in style in the middle years, and a keystone shape, or 'wing' on later versions.
- The lesser 6-string models, such as the DM Mahogany series, had open-backed, 3-on-a-plate non-adjustable "economy" tuners in the earliest years. Later ones, were individual machines, but looked exactly the same from the front.
- The 12-string models had open-back "6-on-a-plate" (non-adjustable/economy) tuners.
- More upscale models, such as the DR Rosewood series, had the same tuners only with chromed cover over them. These were all 'non-adjustable' and held in place by two opposing screws (corner to corner) on the back of the headstock. Styles of this type are still available today with only minor differences.
- Early Rosewood series model 12-string guitars (pre-1975) had non-adjustable covered "6-on-a-plate" ala' Kluson style tuners. Later versions (approximately 1973 onward) were individual, non-adjustable, as on the 6-stringed models (14:1 ratio.)
- Many 6-string "upscale" models from 1981-1983 instruments had adjustable sealed tuners, but the 12-string models continued with the covered (non-adjustable) "economy" tuners (14:1 ratio.) Others continued on using the cheaper tuners.
- The earliest sealed tuners, as early as 1972 (e.g. DR-9, DR-11) had a 6-sided cast body and no brand name (11:1 ratio,) while there were others later on that more resembled Schaller (stop screw to the inside, Schaller style buttons.) or Grover tuners (stop screw below but without the familiar crescent knob.) Few of these sealed tuners were branded at all, while others in later years show "Sigma" stamped on their backs.
Made in Japan Models
- CS-6 Classical guitar. Mosaic marquetry around sound hole. Rosewood bridge. Spruce top. Back and sides laminated bubinga wood. Mahogany neck. Rosewood fingerboard. Pearloid buttons on tuners.
- CR-7 Classical guitar. Mosaic marquetry around sound hole. Back and sides laminated rosewood. Top made of finest close-grained spruce. Carved peghead. Neck mahogany. Flat-oval neck. Top and back binding black and white. Lacquer finish.
- DM-5 Dreadnought. Laminate spruce top. Laminate mahogany back and sides. Black binding (b/w/b/w/b.) Natowood neck. Unbound rosewood fingerboard. Nickel-silver frets. Open in-line tuning machines. Adjustable rosewood bridge on earliest examples. Adjustable truss rod through peghead from 1970 through 1979. Unbound peghead. Open tuners on early models. Covered "economy" tuners on later ones. High Gloss finish.
- DR-7 Dreadnought. DR-7 Dreadnought. Laminate spruce top. Laminated rosewood back and sides. White binding on body (w/b/w/b/w.) Rosewood overlay on peghead. Peghead bound in white. Adjustable truss rod through peghead from 1970 through 1979. Rosewood bridge and fingerboard. Adjustable rosewood bridge on the earliest models. Pearl/pearloid inlay position markers on fingerboard. Chrome closed back tuners (11:1 ratio.) The first year is known to have a zero fret. High gloss lacquer finish. Truss rod adjustment location is on peg head at nut until 1980. After 1980 truss rod adjustment is located internally and is accessed from soundhole.
- 52SDR-9 Dreadnought (c1972.) Solid spruce top. Laminated rosewood sides and 3-piece back with a contrasting rosewood center strip. White binding on body (w/b/w/b/w.) Rosewood overlay on 1st generation "Spatula" headstock (Sigma w/Σ logo.) Headstock and fretboard are single-bound in white. Adjustable truss rod through peghead. Rosewood fingerboard. Non-adjustable rosewood bridge. "Snowflake" (more similar to a Maltese cross) pearl inlay position markers on fingerboard. Chrome closed back tuners (11:1 ratio.) High gloss lacquer finish.
- 52SDR-11 Dreadnought (c1972.) Solid spruce top. Laminated rosewood sides and 3-piece back. White/pearl binding on body (w/p/w/p/w.) Rosewood overlay on 1st generation "Spatula" headstock (Sigma w/Σ logo.) Headstock and fretboard are single-bound in white. Mother of pearl trim throughout ala' Martin D-41. Adjustable truss rod through peghead. Rosewood fingerboard. Non-adjustable rosewood bridge. Mother of pearl Hexagon & heptagon inlay position markers on fingerboard. Gold plated closed back tuners (ratio unknown.) High gloss lacquer finish.
- DJ-7 Dreadnought. Laminated spruce top. Laminated brazilian jacaranda sides. 3 piece matched grain jacaranda back with marquetry. White binding on body (w/b/w/b/w.) Peghead bound in white. Ebony fingerboard. Mother of pearl inlays on fingerboard. Fixed ebony bridge. Natowood neck. Adjustable truss rod. white/black/white binding. Satin lacquer finish.
- DM12-5 12 String Dreadnought. Laminated spruce top. Laminated mahogany back and sides. black binding (b/w/b/w/b.) Rosewood bridge (some 'ebonized') and fingerboard. Unbound peghead and fingerboard. Pearl/pearloid position dots. Open inline "6-on-a-plate" tuning machines. Covered "economy" tuners on later examples. Adjustable rosewood bridge to approximately 1975, non-adjustable thereafter. Adjustable truss rod. Earliest models had a zero fret.
- DM12-7 12 String Dreadnought. Laminated spruce top. Laminated rosewood back and sides. White binding on body (w/b/w/b/w.) "Ebonized" (blackened) rosewood bridge and fingerboard on some, natural rosewood on others. Peghead and fingerboard bound in white. Pearl/pearloid position dots. Adjustable rosewood bridge to approximately 1975, non-adjustable thereafter. High gloss lacquer finish. Adjustable truss rod. Covered "economy" tuners. High Gloss finish.
Earliest models had a zero fret.
- GCS-6 Grand Concert. Laminated spruce top. Laminated mahogany wood back and sides. Black binding (b/w/b/w/b.) Mahogany neck. Adjustable rosewood bridge. Peghead bound in white. Rosewood fingerboard. Adjustable rosewood bridge. Adjustable truss rod.
- GCS-7 Grand Concert. Laminated spruce top. Laminated mahogany back and sides. Black binding (b/w/b/w/b.) Rosewood fingerboard. Adjustable rosewood bridge. Gloss lacquer finish. White bound peghead. Adjustable truss rod.
Additional Models Approximately 1975 to 1978
Some of these guitars still had the early peghead logo, instead of the "Second Generation Sigma" Martin style logo that started in approximately 1976.
- DT-22 Dreadnought. Spruce top. Laminated asian chestnut sides and back with matching wood veneer on Martin style peghead. Solid spruce top. Tortoise shell binding around back and sides. Black pickguard (later examples have Tortoise shell pickguards.) Fixed bridge, some with diamond shape inlays. Fingerboard has snowflake and diamond shape inlays. Pearl "SIGMA" block inlay between 19th and 20th fret. Later examples have gold plated, Sigma embossed Schaller style enclosed tuners (ratio unknown.)
- DR-7S Dreadnought sunburst. Martin style peghead bound in white. Spruce top. Rosewood back and sides. Rosewood fixed bridge. Adjustable truss rod.
- DM-5S Dreadnought sunburst. Unbound Martin style peghead. Spruce top. Mahogany back and sides. Rosewood fixed bridge. Adjustable truss rod.
- GCS-4 Grand Concert. Martin style peghead bound in white. Spruce top. Mahogany back and sides. Rosewood fixed bridge. Adjustable truss rod.
- CS-4 Classical Guitar. Spruce top. Mahogany back and sides. Mahogany neck. Rosewood fingerboard and bridge.
Sigma produced numerous "DR-*" models from the mid-70s on through 1984: DR-8; DR-9; DR-11; DR-14; DR-15; DR-28; DR-28S; SDR-28; DR-35; DR-41; and DR-45. The very rare DR-14 was often confused with the DR-41 but it was a different model. They have a 3 piece back, and the fret markers are different as well. These rare, hard to find models were actually made in Japan and imported to, and guaranteed by Levin in Sweden. They cost more than the top of the range DR-41 at the time. They have a paper label stating this and "Sigma Guitars" "est 1970" is inlaid on the headstock in abalone. There is a DR-14 on display in the Sigma Museum in Munich,Germany.
Special and Unusual Models
From 1980 through 1983, prior to construction being moved to Korea, Sigma produced several models that included electronic pickups: SE-18;SE-19; SE-28; SEMC-28 (with arched back); and SE-36. These models have saddles with each string individually compensated, yielding superb intonation. These models were produced in very limited quantities.
In 1980 Sigma produced the D-10 Anniversary model to commemorate 10 years of Sigma production in Japan. Essentially a gussied up DM-18, the D-10 has a solid spruce top with "matched" (re: laminated) mahogany sides and back, rosewood fingerboard with diamond and square position markers, mother of pearl band inlay stating "Anniversary" between the 19th and 20th fret, tortoiseshell type pickguard and binding, and close-ratio tuning machines. This limited production run lasted one year and this model remained on Sigma Dealers quarterly price lists from October 1980 until July 1981. It is not known at this time just how many D-10's were built but it is believed by some, and indicated by the number up for saleat any given time that production ran into the thousands, not limited to 100 as previously rumored. They were only made in 1980, but throughout the entire build year.
A recently uncovered C.F. Martin memo dated August 7, 1980 further discusses 'economically uncorrectable' cosmetic flaws in the D-10 and how they were to be indicated by the inspectors: "The flawed instruments were graded into 2 categories depending on the nature of the blemishes and were stamped on the back center strip accordingly.
- The D-10 '9' had cross grain sanding marks, finish runs and/or a rough finish, rough or chipped inlay and/or bindings, poor repairs, small indentations and/or discolorations.
- The D-10 '8' had finish checks, shrunken end pieces, filler discolorations, dents and/or a very thin finish.
- Instead of 'seconding' these by labeling them as 'Picador' guitars, and/or voiding the warranty completely, Martin decided to invoke a warranty exception and lower the price by a few points. The affixed warranty card was amended to read..."Your D-10 '9' (or D-10 '8') is not warranted against cosmetic defects."
In the years of 1981 & 1982, Martin imported partially assembled Sigma guitars from Japan and the assembly was completed in Nazareth, Pennsylvania. There were only two models, labeled "Sigma Martin USA DR-28N and DR-35N," "N" for Nazareth. A Martin factory sales brochure shows the DR-28N retailed at $600.00 and the DR- 35N retailed at $650.00 The DR-35N had a 3-piece laminate rosewood back and sides and a solid spruce top. The DR-28Nhad a 2-piece back. The DR-35N had additional detail on the fretboard. The original factory brochure also states components were processed and finished on the same production line as regular Martins. The peghead logo reads "Sigma Martin USA" and inside the sound box is on the neck block " made in USA" with Martin address etc. Some consider the DR-35N to be a prototype of the inexpensive laminate Martin Shenandoah line of guitars, later to become their current HPL (High Pressure Laminate) line of laminated bodied guitars. Since these models had serial numbers ranging from 900,001 to 902,908,. it appears only 2907 of these Sigma Martin USA guitars were ever produced in total, though there may have been others that did not make final inspection and hence were not serialed (I personally know of one such Sigma-Martin,) and are the only Sigma related serial numbers publically available from Martin at this time.
- Official Webside Sigma Guitars
- sigma guitars
- Sigma Catalog, dated June 1, 1974
- Sigma Catalog, date not listed, but prior to 1979 Second Generation.
- Tōkai Gakki
- correspondence with C.F.Martin Guitar Co, Inc. Customer/Consumer Service Department, December 2008
- Sigma catalog, January 1984