The DB5 in Goldfinger (1964) had revolving licence plates. A cursory Google search comes up with some shady websites that sell similar tech, but it would be a nice DIY project to make a licence plate screen that can be changed on the fly (e-ink based maybe). Has anyone tried it?
A really good hack to get around the fact that motor vehicles are by law easily traceable is to...just take mass transit.
Even with paper tickets, if you paid with a credit card there's now a perfect record: Jim Smith got on at the Fruitvale station and got off in Fremont, stayed there two hours, and then came back the same way.