Consider that you and your sign may be plastered across TV and Internet for time and eternity... Dress, act and represent the 2A cause in such a way that you'll be proud of such images.
Watch out for rabble rousers. Don't put it past the anti's to seed a crowd with one or more. It's an easy way to get a crowd to show their asses off for the press.
Sage advice there. Clean cut, calm, bearing a reasoned message focusing on crime and criminals instead of guns will carry more with the fence sitters and scared soccer-mom/dad types than military kitted out people ranting about tyranny and rebellion.
This is an opportunity to change peoples minds, not express anger, play dress up, and pretend at some fantasy.