Why?

I am looking for a sign that I can operate from the steering wheel to tell tailgaters they are dangerously close to hitting me. I suspect all the ones that spring to my mind are probably too crude. But perhaps just a large red neon sign asking "Why?" might slow down the super-charged motorists on the highway around here. Perhaps not. But it would certainly ease my anger at not being able to do anything when the steamrollers (disguised as BMWs and Cargo Vans) start sitting on my bumper. (Sign update: I have hand printed a sign saying "drive safe." It is a complete rip-off of a hand printed sign I saw last week saying the same thing that was on a car from Michigan. Being an Ohioan at heart, I growl when I see most Michigan-der cars because of the grudge between the states dating back to the Toledo War. But when I see a good idea I don't care where it is from ... I use it too. Besides, us Ohio/Michigan types have to stick together here on the east-coast. And the driver had dog rescue stickers on the car as well as peace now bumper stickers. So a kindred soul.)