Assuming the penalties for bringing in a gun are low, "oops, I forget, sorry," all you need to do is send in a train of people with different types of attacks and note which make it through.
A quick check (ETA: of Nevada law) shows that "gunbuster" signs don't have force of law. Assuming you leave if and when asked, there's absolutely no legal repercussion to ignoring them.
http://codes.findlaw.com/tx/penal-code/penal-sect-30-06.html
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.
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).