Most experienced cyclists will acknowledge another cyclist either by a head nod (my method) or a finger wave. Hands off handlebar waving towards another rider can be dangerous. I had a friend two weekends ago do just that and ran into a car. Your body and bike will turn towards the wave. I also believe many people are not purposely ignoring you. They just got caught up in riding. I tend to zone out and see nothng but the road. Do try the head nod next time and if you get a result.