Why would you remove your gun in response to a "no gun" sign on a store rather than merely make sure it's adequately concealed? What's the worst that can happen- they ask you to leave?
In Maryland, 100%Yep. The only time those signs carry legal weight is if you refuse to comply with being asked to leave.
I believe Texas has the '30.06' signs, that put you in deep kimchee if caught.
Again, in Maryland, just leave.