Security van warning?

Have you ever noticed on the back of security vans it says something like "There is a safe in this vehicle, which the guards have no access to".
So why is it there then? Why not just leave it at base?
Answers:
why tell people there is a safe at all. isnt that just drawing attention to it.
The idea is so that authorised personnel at the places of delivery have the code/key/combination with them, so that the drivers are just that, DRIVERS.
throw the jew down the well
Because the guards can put things in the safe through a special type of door but it can only be opened back at the base
What? and carry the safe up the M6!!
What a daft question! The guards are able to put items INTO the safe throughy a special hatch, but cannot take anything out. As it's a security van I think most people would assume there's a safe in it!!