I went for a short ride after church and was reminded of how bikers communicate while we ride. Hand signals were developed long before Bluetooth and radio comms sets became almost required riding gear, and many are still used today.
First, most motorcyclists "wave" when passing other riders. While some only wave at riders on similarly styled bikes and even makes, many others wave to everyone. This is especially true here in Southern California, where, despite year-round riding weather, we are often the victims of pre-occupied drivers, overcrowding and constantly shifting lanes that expose ruts and rain grooves at risk to our safety. Most often the "wave" is more a pointing-either out or downward. Some CMA'ers I ride with took to pointing up with one finger, like the old Jesus Movement hippies did 4 decades ago. This also works when riding in a group-as the downward angle point could confuse following riders that something is in the road.
Signal two is a "head's up" signal. Tapping on the side or top of the helmet means a police officer is waiting ahead of the rider you are signaling. I've never heard a polite distance to stop giving this signal and welcome comments. One time I received the signal but was over 3 miles from the cop on a busy California freeway. While I appreciated the warning I had about 10 other riders give it to me, all the while wondering if the cop was rolling up ahead instead of stationary. The CHP officer may have been in on it-by the time I finally reached him I swear he was laughing at each bike that past!
The third signal I used today was an ok while I rode past a stopped bike. I normally try to stop, but couldn't safely. So I threw out a quick "OK" while glancing back in my mirror. The rider was still astride his bike, and quickly threw back the OK so I wouldn't stop or try to turn around and come back. That's because stopping to help a stranded fellow rider/biker is also part of the code of the road if you feel it's safe. Even if it's only to ensure they have a phone to call for help or a truck, it's something many of us do.
I know there are many others, but these are the three I used today on a ten mile ride. I hope this helps if you aren't familiar yet with all the hand signals. Ride safe!