I can see this ending in a not-so-good way. It's all fun and games until someone uses the marquee tag (they've already used it). Cool idea, but you can't trust the internet as a whole to always do the right thing in situations like this. Kind of reminds me of this burger place a friend worked at, they had a few around the place with TV screens displaying Tweets. You Tweeted and they literally showed up on the screens at all store locations, they weren't checked or anything which made for an interesting situation when a competitor started advertising their own company through the burger chains account in-between people Tweeting profanity and jokes like, "Don't eat the secret sauce, it's not mayonnaise".
It'll be interesting to see how quickly this gets out of hand. Good luck.