FIGlet is a program for making large letters out of ordinary text

FIGlet prints its input using  large  characters  (called FIGcharacters)
made  up  of  ordinary  screen  characters (called sub-characters). 
FIGlet output is generally reminiscent of the sort of  signatures many
people like to put at the end of e-mail and UseNet messages.  It is also 
reminiscent of the output of some  banner  programs, although it is 
oriented normally, not sideways.

The homepage of FIGlet shows some examples of this.

Homepage: http://www.figlet.org