Yep, concealed means concealed!
So the signs hold the weight of the law, and you would encourage people to then trespass?
The signs do not hold the weight of law, in my opinion (not a lawyer). In order for them to carry the weight of the law as your "notice to leave" they would need to be reasonably visible to all visitors. Every entrance, large enough to be seen. If a business were to post the signs on a billboard, then ask you to sign a sheet of paper saying you read the rules of admission, then maybe. In reality, the signs are barely visible, and if you arent looking for them, you can miss them. Is it your responsibility to be looking at them? Perhaps, but even still, they could be missed.