Great idea Austin!!
I think for sure that idea can be played out on a local level. Will you be in college in spring of 08? Here's what I suggest: join whatever group or committee sponsors the DOS at your school. Suggest the T shirt idea to them - my bet is, any LGBT group doing DOS will love the idea. As far as I understand it, each local student group decides what their DOS is going to look like.
I've participated twice and don't feel that it made much impact, but that's largely because the responses I get kinda go:
"Hi Zerbie, how are you?"
Zerbie smiles brightly and nods.
"Oh! You're not talking today? Uh oh - your voice? You're on vocal rest! What's wrong? Laryngitis?"
Zerbie shakes head vehemently and smiles, points to T shirt.
"Ohhhh!!!! Today's the Day of Silence?!"
"Oh God I forgot! I gotta go get my tee shirt!!"
Never linger too long with the ignorant,
throw stones at their talk.
Walk only with the lovers,
the mirror of the soul gets rusty when
dipped in muddy water.