This is why people who routinely carry need training. They must understand their weapon, the law, first aid, and what to do in a defensive scenario. Many legislatures purposely make it burdensome, meaning if you live in a state with weird laws, you need to know them.
I don't know of too many stories of a good guy getting popped in confusion.
Most red states have preemption and clarification laws that regulate where guns can be restricted. So if a liberal powerhouse donor owns a mall chain and puts fancy signs up, it doesn't mean much. It does mean if someone were to identify you as carrying, they could ask you to leave, and you would be trespassing if you didn't. Without knowing it, I'll bet you routinely walk past guns in the grocery store, gas stations, malls, and more.
Personally, if I am carrying, I don't give a shit about a voluntary sign on the door. The bad guys sure don't either.