Let's look at another side of that coin:
You and some other customers walk into a bank. All of you are oc. How many tellers would panic and hit the button thinking that you and the others are going to rob them? It may take a very long time (years) before the scenario your put forth would happen without raising fear and panic. I'm thinking that if tellers are like most J.Q.Public citizens, they don't even know the carry laws of their own state. I'll not raise a fuss if you want to oc in a bank, but I'm not going to be a test case. Imho, the stealth mode would be the more prudent of the two carry methods in that type of establishment. Just my .02 worth.