Check local ordinances before showing up in a mask. Some cities have legislated against this, thanks to the anti-globalist occupy types and their window smashing in Guy Fawkes masks.
Not a Guy Fawkes mask, but an 0bama mask (a couple of Nixon masks to make it bipartisan). Just think of the delicious irony. Arresting someone in an 0bama mask, now that would probably be illegal.