San Rensho 

In a life or death, left hook, right hook situation, I'm not going to get distracted by sounding a horn, I'm going to concentrate on riding and not getting hit. Most cases of near misses with me is not a case where people don't see me. They know I'm there and they intentionally cut me off because they are in a car, I'm on a bike and they are bullies. Sounding a horn of death will not change their behavior and suggesting, in a loud voice, where they can stick thier Hummer is much more satisfying.

I do use a "ring-ring" bell to announce my presence. The signature tone is almost universally recognized. I've had pedestrians in front of me move over and they never even looked behind them, since they knew exactly what was behind them.