About that whole "who other than Genma used a sign before" question, it
happened in Part Four #3 of the Viz translated manga.  It happenes when
Ranma holds up signs to Happousai saying, "You lecherous old fart!" and
"I, Genma Saotome, will bring you to your stupid, perverted old knees!"

Does this count?

 Geoff Tebbetts					   *  Lesson No. 2.
 gt0673a@prism.gatech.edu			   *  The Blue Aura. The
 Instructor, The Akane Tendo School-of-Hard-Knocks *  key is to intimidate
 Magnificent Expert of the Interdimensional Mallet *  the opponent, while
 Originator of the Blue Aura of Anger	           *  trying not to set off
 Akane Tendo's Personal Punching Bag		   *  smoke detectors or
 Hikari @ AnimeMUCK; Daisuke @ RanmaMUCK 	   *  sprinkler systems.