My understanding is that a no guns allowed sign is in no way a law. The worst that can happen is they can refuse to let you enter or ask you to leave, which they can do if you break any of their rules...such as no shirt, no shoes, etc. If a business has no shirt, no shoes, etc they can not have you arrested for entering without a shirt but they can refuse you entrance or ask you to leave. If you refuse to leave, they can call the police and have you removed at which point, an officer will come and ask you to leave. If you refuse, then you can be arrested but none of that has anything to do with your carrying a weapon, per se.