Don't count on someone having to prove ownership to get keys made. My 450SEL was stolen by someone 'lifting the VIN' (getting keys made without proving ownership). I was told by the police that since I parked my car at the train station every day it was an easy target. The thieves write down the VIN from the windshield, get keys made by an unethical locksmith (or employee at a dealer) and come back a few days later to drive off with your car. This was in 1997 and the car was 20 years old! A few parts were taken off and the car was abandoned in the Bronx. My car wasn't that nice before, but I guess someone needed new taillights for theirs.

I now live in CA and have a 560SEL. I'm thinking of changing the locks just for this reason but so far I don't park my car in a public lot on a regular basis (thieve needs to be able to find your car a couple of days later after key is made).

Sorry for the digression.
~Dave