I mean, it wasn't obviously ONLY my idea, but years and years ago I thought to myself, "I would really like it if our cars had programmable message boards."
I realized, of course, that maybe they'd have to come with preset templates, so as not to allow the idiocy of bumper-sticker culture to cause "I disagree with your position and thus will use my car to ram you into the median now" kinds of accidents. The messages could be templates like:
- Please be a more courteous driver
- Your turn signal is on
- I am single: my phone number is 555-5555
- I am lost, be patient with me.