every car has a hand full of vin numbers hidden in them for this reason. They are etched in and painted over so they are invisable, hidden inside closed frame rails between stiffeners and barriers so you cant just stick a camera in and look, you have to cut a section out of the car where you know its located. Its actually pretty cool how they do some of that stuff.
Sadly, thats only usefull, AFTER they find a stolen car or part. And then I guarentee you anyone doing that high end of a crime isnt the guy selling the part to someone on craigslist, so have fun tracing it back even with the stolen part in an investigators hands.