I recently saw a commuter with a whistle hanging around his neck. It was a weird intersection where the bike path is shielded from view from the parallel freeway exit, then when the bikes emerge, everybody has to wait at the same light. He used the whistle to get peoples' attention before chancing the intersection, which is surely smart, because that off-ramp is full of people that have been commuting at 60mph for the last half hour, and expect to be able to roll the red light, turn right and get up to 60mph again.