You know, it's only legal if the use the exact verbiage as directed by the state and not just "No concealed guns". At least that's the way it is in Texas.
In Florida when they passed their CHL, many businesses, put up signs saying no concealed weapons. Well some lawyers started making calls telling them that if there clients were injured or killed because they (the store) denied their clients their constitutionally guaranteed right to protect their person that they (the store owners) would be liable and would be sued for damages.
The signs started coming down. Very effective and true. Just a thought to look in to.
As long as they don't have metal detectors up, who's to know!