Great idea. Maybe you should ban them. That way, nobody will come in and shoot the pla— oh, wait a minute...
I can see the psychotic thought process now... "Yeah, I'm ready to go kill dozens of people...what, bringing my weapons into the posted business would be a $500 fine and misdemeanor? ... Oh, ok, I sure don't want any part of
that! I'll go play with my naval some more then..."
All these signs do is disarm law-abiding citizens, and mark the target zones for terrorists and psychopaths.