Idea Seven: LED programmable bumper sign

You get a small LED sign, maybe a little bigger than a bumper sticker, that you can attach to your bumper. The messaging is controlled by an app on your phone.

Additionally, it could come with a sensor that detects when someone is following you at an unsafe distance. That would trigger an automatic message like "please follow at a safe distance"

Different drivers from the same household could have different preset messages.

Messages should be programmable via voice control.