I make it simple on myself. If the sign contains "30.06" and "Subchapter H, Chapter 411" anywhere on the sign, I presume they don't want my business and move along. I don't speak or read Spanish and therefore don't care what that part of it says.
Although I could probably afford legal costs, I'm not rich and would rather keep what I have rather than spend it on defense that has a weak argument to begin with.
I've watched these arguments take place on this and other forums, gun shows, ranges, etc., and I'm always wondering why?
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They're telling you in explicit terms they don't want your money. It's fun to argue sometimes though...
My 2 cents...