Not federal but at the state level there are such statutes.
He could also run afoul of any CCW laws that apply to the area.
Any such statue would, of necessity be extraordinarily vague. Any lawyer that would allow his client to be convicted under such a statue should be disbarred. I'd still be interested in any specifics that you might know of. I would have to wonder where the 'Hello Kitty AR-15' would fall under such a law.
I do not trust any official elected to office to “faithfully uphold the Constitution” as they are sworn to do.
It is public opinion that drives them, not the letter of the law.
As for the Hello Kitty AR it would get special treatment: most likely Patriot Act - Terrorism. Although exactly who would be terrorized is debatable.