I have heard of people putting big truck horns on their motorcycles, and people look around for the truck, and dont see any trucks, and still hit the motorcycle.
Something to be aware of. Humans have very fast pattern recognition, and most people dont know what a motorcycle horn "sounds like".
From my own experience to avoid an accident Im on the brakes or steering my way out. By the time I decide to blow my horn at someone the danger is already over.
Keep in mind also, Deaf people are allowed to drive, engage in the evasive manuvers first, then the audio exchange.