...but in the event it was discovered, you could be charged with a misdemeanor and lose your concealed carry license. Bend over to tie your shoe have the wind blow your jacket open as you enter a store, and the fact that you're packing might no longer be a secret.
The best course to follow is to respect their right to post such a sign, take your business elsewhere, and let them know why you're taking it elsewhere. Two major retailers in the area removed their signs when they realized that it was costing them business.
They likely won't know....