I may be the odd one out, but I feel that "ride your own ride" entails that you navigate the visual terain and not depend on your co-riders warnign of cops, oncoming cars, etc. Having said that there is one that I use which doesn't require taking hands of the bars. If I do a safe pass and can see more of the oncoming lane than the riders behind me, I will stay in the opposite lane to give the following riders a better feel for how clear the oncoming lane is. Then they can pass and we can keep the group together.
.....a thumbs up to acknowledge another rider's antics......
Ian, I understand what you're saying about not relying on others for signals, but I'm curious: when riding ahead of others do you point out roadkill/deer/farm equipment if you come up on it?
I also will tap my brakes several times if I have to slow unexpectedly or there is a major hazard like a tractor in the road. Brake lights are the best warning signal out there in my opinion.