Maybe something like #XMF4ever or #SaveXmenF4. I've tried to get the #MutantAndProud hashtag trending a few times, but I'm a complete nobody.
For NYCC, maybe someone can print up flyers or pamphlets or hold up signs that say #XMF4ever.
I also created a TinyURL link to the petition. I don't know if there's another way to get this trending, but this can help with the link I guess.
http://tinyurl.com/XMF4ever