The security of safe deposit boxes is a lot more than non existent; banks stake their reputations on providing that security.

You generally need to prove who you are (ie that you are authorized to even enter the room with the deposit boxes) and have a key to gain entrance to your box; if you lose the key, the bank doesn't just have another to provide you - they need to drill out the lock. They're pretty rigid on that. If you're not the box holder, then you better be the named executor or trustee of the person whose box it was.

For that reason I disbelieve that authorities would be interested in OPs small amount of Bitcoin, and if they were, it would be readily apparent that they'ed been there, as your lock would either be drilled out or yourbkey wouldn't work.