That kinda reminds me of the
“day without an immigrant” boycott from a few years back.
I never had anything like that in my high school- but that was 10 years ago. Plus, I think I was one of maybe 3 (openly) queer students; there wasn't much sympathy for the cause, to say the least.
But as for the “Day of Silence”- I think it's the kind of thing that's probably more effective if it's promoted or advertised beforehand- if you can't
explain why you're silent (because you're being silent) or people don't expect it, it comes off as pointless or confusing. I mean, I guess you could wear a sign or something?
I used to be pretty involved with organizing protests and stuff like this- it's especially difficult in small communities, where you don't have the strength of numbers to get your point across. But sometimes if you contact local media in advance and let them know what you're up to, they'll cover it. Those jerks love the “kids are taking a stand against ____” angle, especially on slow news days. ;)