sig block: /sig blok/ [UNIX; often written `.sig' there] n.

:sig block: /sig blok/ [UNIX; often written `.sig' there] n.
Short for `signature', used specifically to refer to the
electronic signature block that most UNIX mail- and news-posting
software will {automagically} append to outgoing mail and news.
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, the}); but many consider large sigs a waste of
{bandwidth}, and it has been observed that the size of one's sig
block is usually inversely proportional to one's longevity and
level of prestige on the net. See also {doubled sig}.
-- The AI Hackers Dictionary

Related:

• sig block /sig blok/ n. [Unix; often written `.sig' there] Short for `signature',
  used specifically to refer to the electronic signature...
• doubled sig [Usenet] n. A sig block that has been included twice in a Usenet article or,
  less commonly, in an electronic mail message. An...
• doubled sig: [USENET] n. A {sig block} that has been included twice in a {USENET} article or,
  less commonly, in an electronic mail message. An...
• sig virus: n. A parasitic {meme} embedded in a {sig block}.
  There was a {meme plague} or fad for these on USENET...
• sig quote: /sig kwoht/ [USENET] n. A maxim, quote, proverb,
  joke, or slogan embedded in one's {sig block} and...
• warlording: [from the USENET group alt.fan.warlord] v.
  The act of excoriating a bloated, ugly, or derivative...
• BUAG: // [abbreviation, from alt.fan.warlord] n. Big Ugly ASCII Graphic.
  Pejorative term for ugly {ASCII ART}, especially ...
• BUAF: // [abbreviation, from alt.fan.warlord] n. Big Ugly ASCII Font -
  a special form of {ASCII art}. Various programs...
• sig virus n. A parasitic meme embedded in a sig block.
  There was...