My lawyer agrees:
If state law says you can't carry somewhere -- like on a school bus, or in a state park -- it's a crime to carry there.
If a sign on the door of a business says "no guns," all they can do is ask you to leave... which, of course, we would all do politely and promptly, right? (Since concealed means concealed, why would THAT ever happen)?
When I go to the Christiana Mall, I always enter through Macy's or J C Penney's. There are no signs at their entrances, or where you enter the mall from the anchor stores.
If the new Target puts up a "no guns" sign, then I guess they don't need my business.