In Arizona there is always a sign on the curve that goes from one freeway to another. It is always yellow and it always says "45". Most people don't know that yellow signs are advisory. They assume it is a speed limit, and then they get on the freeway still going 45 MPH. Honking at them has no particular effect, except that they might honk back. And if you complain to any official person, the response is always "What, you think it should be higher than that?"