I have considered instituting a motorcycle style wave when I pass bikers. Who knows it might catch on. The only issues are crashing due to having 1 hand on the bars and in some places there are so many cyclists I would be perpetually waving.

On a sidenote one of the guys I ride with also rides motorcycles. He ran his own little experiment with waving at motorcycles while he was on his bike. Most waved back though presumably out of reflex. One guy saw the hand shoot out and got his hand off the bars to wave. They he realized it was some guy on a flippin bike. The hand shot back to the bars and eyes glued straight ahead. It was hilarious.