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

BUAF
 //, n.

    [abbreviation, from alt.fan.warlord] Big Ugly ASCII Font ? a special form
    of ASCII art. Various programs exist for rendering text strings into
    block, bloob, and pseudo-script fonts in cells between four and six
    character cells on a side; this is smaller than the letters generated by
    older banner (sense 2) programs. These are sometimes used to render one's
    name in a sig block, and are critically referred to as BUAFs. See 
    warlording.


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

BUAF

   [alt.fan.warlord] Big Ugly ASCII Font.  A special form of
   ASCII art.  Various programs exist for rendering text
   strings into block, bloob, and pseudo-script fonts in cells
   between four and six character cells on a side; this is
   smaller than the letters generated by older banner programs.
   These are sometimes used to render one's name in a sig
   block, and are critically referred to as "BUAF"s.  See
   warlording.

   [Jargon File]