Us "biker" types have smaller sticky thingys which are called helmet stickers. Here are some:

Damn, I got old quick!

Men are like tiles, if you lay them right you can walk on them forever.

I'm a schizophrenic and so am I

$15,000 and 15 miles don't make you a biker

I'm home, take me drunk!

My favorite all time bumper sticker, seen on the back of a pick-up, up there in Wyoming (kat):

Hippies are living proof that cowboys screw sheep

also seen in Wyoming on the back of a pick-up: Cowboy Cadillac

My favorite "vanity" plate comes from California. I saw this while riding over in Marin County, on a Rolls: GREED

Many of the helmet stickers are outrageously obscene, all part of the "biker" mystique, no doubt but the good thing is many are printed on reflective material which allows the motorist to realize he is about to hit a motorcyclist!

CB