sigmonster

sigmonster
 n.

   [common] A beast that randomly chooses one of a selection of
   signatures for appending to mail and news messages. The creature is
   most often mentioned directly when it has been in particularly good
   form and selected a signature appropriate to the topic being
   discussed; the construction "P.S.: good sigmonster, have a cookie" is
   not uncommon. While the are sigmonster programs floating around on the
   net, most hackers who keep one use a silly little Perl or Python
   script that they threw together in the middle of the night under the
   influence of far too much caffeine.