I replaced my horn with open pipes, and, the little four makes more noise than a twin.. It is fun around town ( on the highway it is ridiculous). Seriously, I have noticed that the "cage drivers" as they have been refered to in other posts, have taken notice to my proximity(sometimes begrudgingly) but none the less... i think there may be something to the "loud pipes save lives" mantra...
Air horns are probably more practicle....