I like to think that all businesses actually know the law, and are intentionally posting a gun-busters sign, or other non-compliant sign, to inform Bad Guys that Their Illegal guns are not welcome there. While intentionally not banning legal concealed carry, because they know we're the Good Guys!
After all, if they
really were
actually serious about preventing carry of weapons into their establishment, they would
at least take a cursory glance to the laws required to do so, and
at most, post a metal detector and security guard at every door!
Anything less than either of the 2 above means, to me, that they really don't actually care, and probably just put up the sign as part of a corporate feel-good signage program, or because they came in the pack of their "Franchise Business Kit" from the franchise owner...
If I'm expected to know, and follow the laws to the T as a pro-gunny, I fully expect the anti's to do the same.