Better still, be even more direct. Don't enter if you intend to rob this bank or kill people. I am guessing that this would be a logical suggestion by those that feel a mask is not a threat. I mean if you forgot to take off your vest full of explosives or feel that there is no problem with bringing your gun into the bank and have absolutely no intention of using either while in the bank, what's all the fuss about? ;~) Now on the other hand, if those people came to the bank and slipped a note under the door indicating that they wanted to steal money or to blow people up, they absolutely should not come into the bank. There is a simple solution for every thing.