As a Motorist
Never pull away from traffic lights hoping to outdo your opponent in the next vehicle. He will always give testimony against you should you have an accident further down the road. Of course if he pulls away first and crashes, it is deeply satisfying to later say he was driving like a maniac.
Remember all motorists carry with them heavy personal burdens, unless they be a bunch of reckless kids joy riding whose parents carry the burden. And when under way and no matter how tempted, do not make faces at other passing cars. Folk on the highway these days generate massive hostilities against the outside world and become extremely unstable, isolated as they are in their own little mobile temples of discontent. They may swerve in front of you, force you off the road or even start shooting.
However should you not be able to control yourself and sneer at a passing motorist and his unpleasant passengers, at the first sign of their retaliatory aggressiveness, smile, wave and blow your horn in salute, then display your sign.
TOURIST
Otherwise keep the corners of your mouth well turned down, and your eyes merely slits.