Not necessarilly bad advice, the guy just said it wrong. THAT sign in Texas is not a legal way to bar anyone from carrying a concealled weapon. Only a 30.06 or a 51% sign can do that, this particular sign is a joke. Oh yes they can ask you to leave but no one is getting arrested or being confiscated, only escorted out and then what about the bill?
In Texas, yes; in other states, no. In many states, that sign would be plenty to have you arrested and charged.