You are in the position of (some) power. By knowingly choosing to to help someone do something unethical, you contribute to furthering unethical behavior. Also, what is the difference between "a jerk ... speaking up" and "an asshole"? Is an asshole still an asshole if their business is legal?
I think you should reconsider your sign. It shouldn't say We reserve the right to refuse service to anyone, it should say Greed is good. Remember, all that is necessary for the triumph of evil is that good men do nothing. Don't get me wrong, there's nothing wrong with making money, but don't try and rationalize your ethics away.