Now that I got the prototype working I'll put the electronics in a box with a 15Ah solar charging powerbank in the back of my car.
I'll stick the LED to my back window. See what happens.
Couple of ideas I'm considering:
1- Hook it up to a distance sensor and show smiley/frowny face on LED based on distance to the car behind me.
2- develop the android app to save designs (requires backend, login things etc.
3- be done with it.
4- overdo it and design pcb and a nice case.