McQuary limit 4 lines of at most 80 characters each, sometimes still
   cited on Usenet as the maximum acceptable size of a {sig block}. Before
   the great bandwidth explosion of the early 1990s, long sigs actually
   cost people running Usenet servers significant amounts of money.
   Nowadays social pressure against long sigs is intended to avoid waste of
   human attention rather than machine bandwidth. Accordingly, the McQuary
   limit should be considered a rule of thumb rather than a hard limit;
   it's best to avoid sigs that are large, repetitive, and distracting. See
   also {warlording}.


Source: The Jargon File