I dunno... I generally tend to respect a business owner's right to discourage me from spending my hard-earned dollars in their establishments.
This.
And I've always equated a GB sign as a "no trespassing" sign. The owner is telling you he doesn't want you in here if you're doing X. Kind of like the banks that prohibit the wearing of hoods, hats or sunglasses inside. Would you also ignore those signs?