Etch your vehicle identification number on car windows and major parts.

FORBES: New Cars With The Highest Theft Rates

Car theft rings clone vehicles by taking license plates, vehicle identification numbers (VIN), and other tags and stickers from a legal car and putting them on a stolen vehicle of similar make and model.

CNN: FBI breaks up $25 million 'car cloning' ring

All those years later, he still had the car's title that listed its vehicle identification number (VIN), which matched the VIN on eBay.

CNN: Texas man finds his car 42 years after it was stolen

On its website, Dataium says it observes more than 20 million shoppers across 10, 000 car websites, although it doesn't claim to have identification information on everyone.

WSJ: They Know What You're Shopping For