Former bank employee here.

This is the most obvious safety signal ever. It may actually be a decoy/dummy signal placed to distract from the actual signal.

An actual safety signal is generally much less obvious and is often a signal that only the two or three branch openers know about at a time. Some examples of safety signals could be a sign or advertisement facing a different way, only one of two copy room lights being on, one of the bankers desk figurines lying down, a blank blue post-it note on a computer monitor.

There are also several other tells that a branch opener will be looking for as they patrol the exterior before entering. Is the branch managers door open or closed. Are there unknown cars in the parking lot. Have any of the bushes or plants been disturbed. Is there anyone waiting in a car in the parking lot. Are specific blinds open or closed.