sig virus

sig virus n.  A parasitic {meme} embedded in a {sig
   block}.  There was a {meme plague} or fad for these on Usenet in
   late 1991.  Most were equivalents of "I am a .sig virus.  Please
   reproduce me in your .sig block.".  Of course, the .sig virus's
   memetic hook is the giggle value of going along with the gag; this,
   however, was a self-limiting phenomenon as more and more people
   picked up on the idea.  There were creative variants on it; some
   people stuck `sig virus antibody' texts in their sigs, and there
   was at least one instance of a sig virus eater.