One of my friends from the Bennington Rally, Touko, has a deer whistle on his Rocket 3. It's not one of those passive whistles that makes sound from the air rushing through it, but rather an electronic noisemaking device that emits a high pitched whistle. If you stand in front of his bike and he turns it on, your ears start to hurt, pretty freaky, but from what he tells me he hasn't had any deer problems since he put it on.
