Double Naught Spy and Peetzakilla: You are right, it could seriously impact a business. Posting the sign is a very good idea.
I have a policy that I do not accept checks from a certain local bank. It has caused a few problems, but we were able to work around them and everyone was happy in the end. I got my money and they got their chickens.
Sometimes we (I) act irrationally and after thinking things through find a better way of dealing with situations. I have explained to my customers why I do not take checks from this bank and the fact there is a branch just up the road that has an ATM.