Once I was thinking of making a sign...really just a dry erase board and put suction cup fasteners on the corners to attach to one of my car windows.
It could display my last tank MPG efforts.

I decided against it because so far I have, no dings, not even one scratch...except where the wife scraped the front wheel against a curb and a couple usual sand-size pits in the front spoiler area.
I take extreme care not to park where other doors can't ding, generally out of the way.

Call me paranoid but for my luck I'll get a nasty long knife scratch down the side for condgradulations if I put such a sign.

Anyone know how the chrome HYBRID lettering is attached to the car body?
If it's bolted or easily removed it would be easy to make a green glowing background with a sheet of plastic and some LED's.

Efficient drivers do it better.
1003 miles a tank personal record. 74MPG calculated. HCH1 CVT