well, I'm not going to bother reading everyone's reply, and it certainly has been said already but, if you have to ask, you probably need a mentor.
I have seen that posting at 100% of gun shops around here for the exact reason you would expect. Some Fu-K-Up shows up with his gun, whips it out, points it around, proclaims its unloaded, and proceeds to clear the very loaded chamber. In the 5 minutes this guy is talking up the counter with no intention of selling his gun he came in to "get an idea of the market", 2-3 real customers have already left, never to return, because no one want to go to "that kinds of place". They tell their friends, and then they're out dozens of customers. Yes, really. If there is a sign, its because someone made it necessary. If you can't understand the sign, there is a good chance your the reason there is one. No offense intended.