Mercedes-Benz's have a pop-out metal clip that can be used to lock the glove and trunk. It's designed to be extract with a simple press so that dropping you car with a valet doesn't require turning off the car to remove it.

Clearly the lock isn't meant to stop a determined intruder. It's more of the "Locks are for honest people" type thing to indicate that you shouldn't be opening the glove or trunk.