This varies from jurisdiction to jurisdiction. It's a crime in Texas for a licensed concealed carrier to carry a gun onto property where there are signs prohibiting the carry of guns.

http://codes.findlaw.com/tx/penal-code/penal-sect-30-06.html

Of course - I should have specified, I checked Nevada law.

That said, Texas law requires very, very specific signage. The last time I was in Austin I saw lots of them, but none that met the legal requirements.

> That said, Texas law requires very, very specific signage.

Exactly right. The amateur signs you see are almost a running joke, to intimidate new CCW permit holders. Here's the full description of what standards a sign must meet to be enforceable: https://en.wikipedia.org/wiki/Gun_laws_in_Texas#30.06_signag...

Bonus, you can carry without a permit, as long as you claim you were 'travelling', and the burden of proof is on the cops to dispute it: http://www.dallasobserver.com/news/texas-concealed-gun-laws-... (this law may have changed by now, but it was widely known when I lived there).

It's the same in Ohio. Most buildings that ban guns don't have the proper signage.