I’m waiting for the bank to open and they have this card facing the street. What is it used for?

I’m waiting for the bank to open and they have this card facing the street. What is it used for?
Answer: It’s definitely a safety signal. We switch ours quarterly and it’s to let other employees know that it is all clear to open. Typically we had 2 employees “open” the branch while the rest waited in the parking lot or across the street for “all clear.” The openers go in, turn off the alarm, search the building and check everything, then set the signal.