|This article relies largely or entirely upon a single source. (June 2011)|
Bag tags, also known as baggage tags, baggage checks or luggage tickets, have traditionally been used by bus, train and airline companies to route passenger luggage that is checked on to the final destination. The passenger stub is typically handed to the passenger or attached to the ticket envelope: a) to aid the passenger in identifying their bag among similar bags at the destination baggage carousel; b) as proof—still requested at a few airports—that the passenger is not removing someone else's bag from the baggage reclaim hall; c) as a means for the passenger and carrier to identify and trace a specific bag that has gone astray and was not delivered at the destination.
The first "separable coupon ticket" was patented by John Michael Lyons of Moncton, New Brunswick on June 5, 1882. The ticket showed the issuing station, the destination and a consecutive number for reference. The lower half of the ticket was given to the passenger, while the upper half, with a hole at the top, was inserted into a brass sleeve and then attached to the baggage by a strap.
At some point, reinforced paper tags were introduced. They are designed to not detach as easily as older tags during transport.
The Warsaw Convention of 1929, specifically article 4, established the criteria for issuing a baggage check or luggage ticket. This agreement also established limit of liability on checked baggage.
Prior to the 1990s, airline bag tags consisted of a paper tag attached with a string.
The tag contained basic information:
- Airline/carrier name
- flight number
- the record locator (a 6-digit code; at one point it was 5 and later 10)
- name of airport of arrival
These tags became obsolete as they offered little security and were easy to replicate.
Current bag tags include a bar code. These bag tags are printed using thermal or barcode printers that print on an adhesive paper stock. This printed strip is then attached to the luggage at check in. This allows for automated sorting of the bags to reduce the number of misrouted, misplaced or delayed bags. The limitations of this technology was apparent at Denver International Airport when a fully automated cart-based system significantly delayed the airport's opening. United Airlines announced in August 2005 that the cart-based system at Denver was to be scrapped. While the inability to reliably read all bar-coded tags in the Denver installation was a part of the problem, it was one of several technical reasons for the delayed opening. Nevertheless, automated sorting of baggage using laser scanner arrays, known as automatic tag readers, to read bar-coded bag tags is standard at major airports.
For flights departing from an international airport within the European Union, bag tags are issued with green edges. Passengers are eligible to take these bags through a separate "Blue Channel" at Customs.
Bar codes can not be automatically scanned without direct sight and undamaged print. Forced by reading problems with poorly-printed, obscured, crumpled, scored or otherwise damaged bar codes, some airlines have started using radio-frequency identification (RFID) chips embedded in the tags. In the US, McCarran International Airport has installed an RFID system throughout the airport. Hong Kong International Airport has also installed an RFID system. The International Air Transport Association (IATA) is trying to standardize RFID bag tags. There is a somewhat higher probability of reading RFID tags automatically. Physically, however, RFID tags are not more robust than barcode tags.
British Airways are currently trialling the use of re-usable electronic luggage tags featuring electronic paper technology. The passenger has to check-in using the British Airways smartphone app, then the passenger holds their phone close the tag and it will transmit the flight details and barcode to the tag using NFC technology. As the tag utilises electronic paper, the battery only has to power the tag when the passenger is sending the data to the tag. 
Qantas introduced Q Bag Tags in 2011. Unlike the British Airways tags, they do not feature a screen which means there is no barcode to scan. This has limited the use of the tags to domestic flights within Australia on the Qantas network. The tags were initially given free of charge to members of the Qantas Frequent Flyer program with Silver, Gold or Platinum status. The tags can also be purchased for A$29.95.
The term license plate is the official term used by the IATA, the airlines, and the airports for the 10-digit numeric code on a bag tag issued by a carrier or handling agent at check-in. The license plate is printed on the carrier tag in bar code form and in human-readable form, as defined in Resolution 740 in the IATA Passenger Services Conference Resolutions Manual (published annually by IATA). Each digit in a license plate has a specific meaning. Contrary to popular belief, the flight number is not encoded in the license plate on the carrier tag. The license plate is an index number linking a bag to a Baggage Source Message (BSM) sent by a carrier's departure control system to an airport's baggage handling system. It is the message that contains the flight details and passenger information, thus enabling an automated baggage handling system to sort a bag automatically once it has scanned the bar code on the carrier tag. Thus these two things are essential for automated sorting of baggage. Note that the human-readable license plate may contain a 2-character IATA carrier code instead of an IATA 3-digit carrier code. For example, BA728359 instead of 0125728359, but the bar code will always be the full 10 digits (0125728359 in the example - 125 and BA being, respectively, the IATA 3-digit code and IATA 2-character code for British Airways). The first digit of a 10-digit license plate is not part of the carrier code. It can be in the range 0 to 9: 0 for interline or online tags, 1 for fallback tags (pre-printed or demand-printed tags only for use by the local baggage handling system if it cannot receive BSMs from a carrier's departure control system due to a fault in the latter or in communication between it and the baggage handling system, as defined in IATA Recommended Practice 1740b) and 2 for Rush tags. The purpose of numbers in the range 3 to 9 as the first digit of the 10-digit license plate is undefined by IATA but can be used by each carrier for its specific needs (commonly used as a million indicator for the normal 6-digit tag number). 
Besides the license plate number, the tag also has:
- Name of airport of arrival
- Departure time
- IATA airport code of airport of arrival
- Airline code and flight number
- Name of passenger identified with the baggage (last name, first name)
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- Mario Theriault, Great Maritime Inventions 1833-1950, Goose Lane Editions, 2001, p. 63. 0864923244
- Patent filing
- [IATA Passenger Services Conference Resolutions Manual https://www.iata.org/publications/Pages/pscrm.aspx] (PSCRM), 33rd Edition, Resolution 740, section 5.1.2; however, this source does not speak to how airlines commonly use that digit. It just says that values 3 through 9 are for "interline and on-line use".