a lock is not to lock

i work at school cafe, so that i use staff lockers all the time.
i discover that even i use a lock to lock the locker,
i can still able open the locker without using a key.
the lock is easy to open when i just push up the door a little bit.

Then, a lock lost its function.
But, it becomes a sign or a warning to other people.
It is a sign that means someone already used that locker,
and it becomes a warning to people to not to open the locker.

the lock lost its physical function,
but it still kept the people away from that locker.
Sometimes, maybe a sign of something is more important than its actual function.