Try your stunt at any drive through and you will get the same treatment.

It is not a simple company policy, it's an insurance liability. If a nutcase drove up and didn't see you STANDING at a Drive-Thru...again...D-R-I-V-E Thru (There's your sign you were wanting) and slammed into you...I'm sure you'd be sitting in a Courthouse somewhere blaming the accident on the bank itself.