The Jargon File (version 4.4.7, 29 Dec 2003):

sig quote
 /sig kwoht/, n.

    [Usenet] A maxim, quote, proverb, joke, or slogan embedded in one's sig
    block and intended to convey something of one's philosophical stance, pet
    peeves, or sense of humor. ?Calm down, it's only ones and zeroes.?


The Free On-line Dictionary of Computing (30 December 2018):

sig quote

    /sig kwoht/ A maxim, quote, proverb, joke, or slogan
   embedded in one's sig block (as used in Usenet news) and
   intended to convey something of one's philosophical stance,
   pet peeves, or sense of humour.  "Calm down, it's only ones
   and zeroes."

   [Jargon File]

   (1994-11-04)