Symbol is one of the four standard fonts available on all PostScript-based printers, starting with Apple's original LaserWriter (1985). It contains a complete unaccented Greek alphabet (upper and lower case) and a selection of commonly used mathematical symbols. Insofar as it fits into any standard classification, it is a serif font designed in the style of Times Roman.
Due to its non-standard character set, lack of diacritical characters, and type design inappropriate for continuous text, Symbol cannot easily be used for setting Greek language text, though it has been used for that purpose in the absence of proper Greek fonts. Its primary purpose is to typeset mathematical expressions.
The font was created by Adobe and has its own character encoding, with the Greek letters arranged according to similar Latin letters (Chi = C, etc.). The document describing the mapping to Unicode code points was created before several of the characters were added to Unicode, so the original mapping assigns several of the characters to the Private Use Area (PUA). A later version of the font by Apple uses more recently introduced Unicode code points instead. The table below mostly follows the Apple mapping.
The characters ®, ©, and ™ are encoded twice: one version has serifs, the other (highlighted in yellow) is sans-serif. The Adobe mapping uses PUA for all six characters to ensure that the presence or absence of serifs is observed, while the Apple font maps the serif versions to the standard Unicode code points and the sans-serif versions to PUA code points (but not the same ones Adobe used).
The character at 0x60 (highlighted in red) does not appear in Unicode. It is described in the Adobe map as "RADICAL EXTENDER", with the Adobe glyph name "radicalex", and is mapped to the PUA code point U+F8E5. It is an over-bar for extending the radical sign over the operands of the radical operator. Some versions of the font implement this as a non-spacing character so that it can be combined (like non-spacing diacritical marks) with the operands it covers.
Beyond the use of Private Use Area code points, Adobe and Apple have a few other minor differences in code point assignments. Character 0x27 (called "suchthat" in the Adobe document) is assigned by Adobe to U+220B (∋, CONTAINS AS MEMBER) but by Apple to U+220D (∍, SMALL CONTAINS AS MEMBER), which more closely resembles the symbol usually used for such that. Characters 0xE1 and 0xF1 are assigned to different sets of angle brackets: by Adobe to U+2329 and U+232A (〈 and 〉), by Apple to U+3008 and U+3009 (〈 and 〉). Apple also introduces the Apple logo as PUA code point U+F8FF for character 0xF0, a position not used in the original Adobe font (and not assigned in the table above).
Lowercase Greek letters appear in italics in many older versions of Symbol. While both Adobe and Apple agree on assigning characters 0x66 and 0x6A respectively to Unicode code points U+03C6 (φ, GREEK SMALL LETTER PHI) and U+03D5 (ϕ, GREEK PHI SYMBOL), some versions of the font interchange these two symbols.
*encoded as ASCII for older versions of the font
The use of the Symbol font in mathematical expressions was part of a W3C recommendation for HTML 4.  At the time of that original recommendation (December 1997), the only native way to display many mathematical symbols in HTML was a direct use of the "Symbol" font. Such explicit references are now strongly discouraged for new documents, but they survive in many existing pages on the Internet. Also, the Symbol font provides graphics that are specifically intended as components in the two-dimensional layout of mathematical expressions. Examples include upper and lower parts of brackets or integral signs and a square-root sign without a vinculum.
Until 2010 or so, the Unicode glyph U+221A corresponding to the square-root sign (the HTML entity is named radic and has decimal code 8730) was usually rendered with a short built-in vinculum. That made it an inadequate graphical replacement for the original character from the Symbol font (itself designed around a slanted line extending all the way to the upper-right corner of the character box, without any spacing). The more recent renditions of the HTML radic entity (U+221A) no longer feature any vinculum and are thus more compatible with the standard graphical representation introduced in the Symbol font. Both styles of the square-root glyph (with or without a short vinculum) have the same disembodied meaning, so the integrity of the Unicode repertoire is not compromised by this adjustment.
Full legacy support of the Symbol font is provided by major modern web browsers like Internet Explorer and Google Chrome. That support involves a specific handling of Adobe's special encoding, which is not properly implemented in at least some versions of other browsers, including Opera, Safari and Firefox. Such browsers do not correctly render legacy HTML documents that make explicit use of the Symbol font.
- "Adobe Symbol Encoding to Unicode". Unicode.org. 30 March 1999.
- "Map from Mac OS Symbol character set to Unicode 4.0 and later". Unicode.org. 5 April 2005.
- W3C (1998). "Introduction to character entity references".