I wish I could find that blog where this young dude had a gps tracker on his car and he found it.
IIRC, that was on Wired.
Ok, that's where I read it:
Busted! Two New Fed GPS Trackers Found on SUV | Threat Level | Wired.com
Caught Spying on Student, FBI Demands GPS Tracker Back | Threat Level | Wired.com