Whenever you see one of those idiotic signs on a restaurant or bar, or, of all things, a bookstore, you should at the very least not patronize the place. What you really ought to do is stand in the door, without entering, and say to the bartender or whoever is in charge (you might have to shout) that it’s been nice doing business with them, but that of course it’s all over now, as their little sign means they no longer want to do business with you. Or write them a letter saying the same thing. And include this URL. Or both.