Here's the plan: I'll ask you nicely to remove your hat and sunglasses to make it easier to identify you. If you don't comply, I'll serve you anyway! Take that, potential bad guy. I'm sure the actual bank robbers will be deterred by "everyone in the bank will be watching them more closely."
About as effective as "(INDICATE IDENTITY OF OPERATOR) BANS GUNS IN THESE PREMISES" signs for stopping criminal violence.