Look... I totally understand where you're coming from- like a lovely girl I met on Monday, she was dressed as Gaara of the Wind from Naruto, and she had a cardboard sign hanging around her neck that said "I'm not dead damnit!" or something of the sort, maybe it said im not f*cking dead- anyhoo, those things like that are cute. Then there was a neko girl who ran up ans asked me for a hug, with a hug me sign around her neck...its cool, fine, but some people do it just for the sake of being obnoxious and just to get stupid attention.
I think there should be a restriction on what you can write, also..hey maybe the con can make some money by getting some of those small miniature white baords and attach some rope on em and sell them for people who want to make sings.. I'm sure you'll make alot- it'll be a good idea for the next con.
By the way, I was dressed as American McGees Alice (the bloody version with a red headband and walking around with her mom xD; ), and I only made it for the last day TT__TT