Comment by plorg

Journalists doing ride alongs have already identified the system and it doesn't really on "restricted databases", they rely on observation and multiple attestation. In any case, there are indeed commercial services for looking up license plate data, and they rely on watching the notices that are published when you register your vehicle. It's the same reason why you receive all sorts of scammy warranty "notices" when you buy a car.

In fact the first clue that they look for is having Illinois Permanent plates because that is a strong indicator that they are using rental vehicles. That doesn't take a database, it's just a strong signal that can be confirmed by other evidence.