So if someone goes to the trouble of posting something that says "Security Notice - Carrying of Concealed Weapons Is Prohibited" IMHO it's is VERY reasonable to conclude they're not really trying to ban CHLers, they're trying to placate the soccer-mommies who think victim disarmament zones are somehow "safer."
Debates on the wisdom of this type of PR move are probably endless, but when I see a sign that's not even close to being compliant, I ignore it - I'm on solid ground legally, and I'm quite sure that ignoring a blatantly non-compliant sign is NOT an indication of moral turpitude.
(Of course, if a sign has 0.95" letters instead of the 1-inch letters called out in the law, or if there's a punctuation mark missing . . . that I'll comply with.)