Assuming you have a bare key on hand—whether it be a house key, mailbox key, or a car key—use its back end in place of a coin. Since the deposit lock is designed to hold a quarter-sized object, a key should fit seamlessly.
So, if the button weren’t on the seatbelt strap, the latch plate could slide to the bottom of the seat belt, making it harder to wrangle and buckle in. Sure, it’s easy to overlook these details while you’re driving, but it’s also nice to know the amount of thought put into our safety.