Not long ago there was a post about an incident in a Walmart where a customer who had a CWP decided to unload his weapon so he could show it to someone. He had an unintentional discharge while unloading. No one was injured but if there had been it's likely that someone would have sued the gun's owner, it's manufacturer and the store. A store with a sign might be able to cut it's legal fee losses by requesting to be dismissed from the suit because they had the sign.