I wave at everything on 2 or 3 three wheels. Even bicyclists, sometimes. If I can't wave (middle of a turn, shifting, sketchy intersection, etc.), I nod. Most people wave back. In this area, it's 50/50 whether Harley riders will wave back. That always cracks me up. Scooters often don't wave back. I think some scoots aren't expecting a wave so don't have time to do it before you've passed them, others (like a friend of mine) don't "get it."
I also give a thumbs up to anyone driving a car I like, and wave at pedestrians in my neighborhood. Usually rev bomb if I'm going by kids, seems to make them happy. If I'm in someone else's neighborhood exploring I'll wave so they don't think I'm a creeper. lol