Signs are signs. People often post signs without having any idea whether or not the signs are legal.
Example: The Veterans Administration. There are two driveways onto the campus of the VA hospital I go to, one off a main street and one off a side street. Sometime early in Obama's first administration, new signs were posted at both entrances to the campus, with the big red circle & slash through a gun and verbiage warning that dangerous weapons are prohibited on the property. The fine print at the bottom cites 18 USC 930.
The problem is that 18 USC 930 says
nothing about guns on the property. It prohibits firearms
in "federal facilities," and it then defines a federal facility as "a building or part thereof owned or leased by the Federal Government, where Federal employees are regularly present for the purpose of performing their official duties."
As it happens, there is a federal regulation pertaining only to VA properties, and that does prohibit firearms anywhere on the property. But whoever posted the signs at my VA facility obviously didn't understand the law. I'm not going to volunteer to be a test case, but I think it would be interesting if someone were busted for having a firearm in his car. His defense would be that he knew 18 USC 930 does NOT apply to any part of the campus other than the buildings, so he assumed that he was okay. Of course, in fact he would have broken the law, but if the VA cites an incorrect law and you know what that law says -- shouldn't you be allowed to rely on that? VERY few people know about 38 CFR ยง 1.218 (
https://www.law.cornell.edu/cfr/text/38/1.218 )