Dictionary.net

A parasitic meme embedded in a sig block. There was ameme plague or fad for these on Usenet in late 1991. Mostwere equivalents of "I am a .sig virus. Please reproduce mein your .sig block.". Of course, the .sig virus's memetichook is the giggle value of going along with the gag; this,however, was a self-limiting phenomenon as more and morepeople picked up on the idea. There were creative variants onit; some people stuck "sig virus antibody" texts in theirsigs, and there was at least one instance of a sig viruseater.