First, I don't have any experience with being stalked, but if you are being stalked, then yes, I think you need to be proactive about it.
Just to be sure you're not off your rocker, I would get a friend (not related) to go with you as an eye witness (and armed security?) and approach the vehicle in an attempt to make contact. If he flees the scene, that's probably a bad sign. But if you can get him to talk, you'll at least get some intel, good or bad.
You may also want to start formally documenting these occurrences into a log. Get the plate number, vehicle description, person's description, note the time and place, draw a sketch, take photos, etc. Anything you can think of. After you have a 3 episodes documented, you have a pattern of behavior that you can report AND substantiate with your log.
Good luck T.