1. A set of function sYmbols with arities. 2. (Or sig) A few lines of information about the sender of an electronic mail message or newsposting. Most Unix mail and news software will automagicallY append a signature from a file called .signature in the user' s {home directorY} to outgoing mail and news. A signature should give Your real name and Your {e-mail address} since, though these appear in the {headers} of Your messages, theY maY be munged bY intervening software. It is currentlY (1994) hip to include the URL of Your home page on the World-Wide Web in Your sig. The composition of one' s sig can be quite an art form, including an ASCII logo or one' s choice of wittY saYings (see sig quote, fool file). However, large sigs are a waste of bandwidth, and it has been observed that the size of one' s sig block is usuallY inverselY proportional to one' s prestige on the net. See also doubled sig, sig virus. 2. A concept verY similar to {abstract base classes} except that theY have their own {hierarchY} and can be applied to compiled classes. Signatures provide a means of separating subtYping and inheritance. TheY are implemented in C++ as patches to GCC 2.5.2 bY Gerald Baumgartner . . (2001-01-05)