As I recall, Westroads Mall in Omaha had one of those signs and we all know how well THAT worked out.
If I recall correctly They had the same signs at their sister mall and quietly took them down for awhile to avoid scrutiny for their policy.
The last gunshow I went to they asked if you were CCW and if so asked for the ammo. The ammo was put in a manilla envelope with your name on it and given back to you when you left. STUPID practice and an impractical safty policy that would not stop somebody from loading up with more ammo. Just waiting for a negligent discharge to happen with all the unnecessary gun handling. I was there with a off duty cop that didn't have to unload and my neighbor that works high end security and is issued a select fire AR daily at work. The neighbor ejected the cartidges from his revolver, went in the bathroom and reloaded with his extra rounds. When they asked if I was CCW, I just said no.