A simple coloured symbol on vehicle licence plates indicating the energy source employed (Gasoline/diesel/electric/hydrogen /over-unity device/Mr. Fusion generator).-- 8th of 7, Mar 04 2017 //Why not // And, at the same time, why?-- MaxwellBuchanan, Mar 04 2017 So those using sticks of dynamite can be given the appropriate distance.-- wjt, Mar 05 2017 A school bus powered by the child passengers pedaling would be classified as corn flake powered in the morning and peanut butter jelly sandwich powered in the afternoon. So a yellow flake and sandwich symbol on the bumper.-- popbottle, Mar 05 2017 random, halfbakery