Surprisingly, the roof of your car is as unique as your fingerprints. The dirt on your roof, the pattern of scratches, the exact SHAPE … all these features and more create a signature that can be recognized by cameras along highways, in toll booths and even from satellites (if they are looking for you). Several states are testing this technology now for use in traffic analysis and considering the technology for a variety of applications including use taxes.
Do you really want data about your travels to be recorded in this way?
I'm not sure what you can do about this, if anything. My recommendation is to wash your car frequently. It is fun and it might help.
REFERENCES:
Anaheim Advanced Traffic Control System Field Operational Test: Technical Evaluation of SCOOT
Evaluation of Infrared and Millimeter-wave Imaging Technologies Applied to Traffic Management
Video Technologies for Roadway Surveillance and Automated Detection