I'm pretty sure it's also in the con book (or, it was last year I think O-o) not to glomp people without permission anyway. It'd be a hassle to give out bracelets/pins to the majority that supports that, and it'd also be hard for a glomper to spot that out before they attack.
I think last year, someone did sell "don't glomp" pins or something, but it's a lot easier to spot out the hug/glomp-me sign holders than the latter
That, and as long as people follow the rules, it shouldn't be too much of a problem...
... Of course, a lot of people ignore the rules |:
If anyone glomps you without permission, teach them a lesson by yelling their ass off about how they could've broken your costume/prop/camera/etc. *u* It'll probably convert them.