Have you recently seen a sign on the road "Honk, if your happy?"?

Yes i have seen such signs, sometimes at the back cars.

If it is during the day and no pedestrians are around and no other vehicles are just in front i would do so - but not otherwise, because it might give the pedestrians a fright and also it might be interpreted differently by the driver in front.

In the case of on the back of vehicles i would just give a honk and a friendly wave if the driver looks back through his/her rear view mirror.

Yes. Mitcham Road Mithcam Vic.

No. Can't be bothered

no but we have a series of signs along a stretch of road here that are split into four signs( to keep people alert) they read: little bo peep \ lost her jeep \ it struck a truck \\ when she fell asleep \ each about a mile apart-cool,huh?

I prefer the one that says:

Honk if you hate ....

Noise Pollution.