Digital car labeling based on driving pattern
You could have a digital bumper sticker that changed colors from a spectrum of colors to reflect the driving habits of that driver or this session of driving.
If the driver exceeds the speed limit it would turn a little yellow. If the driver makes sudden stops or sudden turns or rabbit takeoffs from lights you can turn a different color. That way you can alert drivers what to expect when this person is driving wherever they are.
When the car stops the device would clear itself maybe save it and do a blog or something and start again with the next driving session.
Could also be useful on trucks to show whether they've been aggressive or that sort of thing. And let all the cars around them know what's going on so that they can react appropriately.
This could help lay the groundwork for autonomous vehicles also because then they would be able to pick up on that data until they need to give a larger buffer around the human driven car to allow for the activity that's been on.