I was on a very loosely managed lower level bike group ride awhile back, it is put on by a bike store and has a rag tag group of participants. One guy was riding behind me constantly blowing a whistle. I asked him why he is doing that, because it is really annoying and makes me think there is some emergency because I associate the whistle blowing with an emergency so I am looking around for the emergency and wondering what the heck is happening. He said he blows the whistle every few seconds so cars will be on the lookout for his bike. I told him that he should not do it, but he didn't listen to me.