actually, in many jurisdictions, it is illegal to honk your horn, unless it is an emergency situation. A couple stories came out last year up here in seattle where a driver got a warning because he honked at a car in front of him that didn't notice the green light.
Here ya go:
http://seattletimes.nwsource.com/htm...bumper16m.html
The other day Mark Cruz, of Renton, was waiting to turn left at a green light in downtown Seattle. The car in front of him was sitting under the light, turn signal blinking, but had not budged even though all oncoming traffic had passed. Cruz honked his horn to urge the driver to move. "Then I was pulled over by a Seattle police officer on a motorcycle. He let me off on a warning for honking at the car in front of me.
"Dumbfounded, I said, 'Of course I was.' What am I supposed to do when someone just sits there at a green light?
"He then told me that use of your horn is only for emergencies."