I remember after "The Dukes of Hazzard" got popular, you could go outside any time and hear a "Dixie" horn. I really wanted my dad to get one for his car, but needless to say, he wasn't interested in doing that. I really wanted one, though.
Musical horns really don't do much except annoy the other drivers on the road. People just aren't programmed to listen for them as a hazard warning. However, they are much less common these days, so they might get a driver's attention. However, getting it in a good way is the object, not startling them into having an accident.