I find the whole motorcycle wave thing very interesting: lots of unexplored psychological/sociological stuff going on there.
When I'd have visitors in a certain rural Missouri county where I lived, they'd always ask me, "Why is everybody we pass waving at us?" I'm not talking just motorcycles, I'm taking every kind of vehicle one would pass.
Only answer I had was "That's what people do here." I've been in other rural counties in Missouri and other states where that doesn't happen so the whole waving thing seems to be based on local social mores. Some country folks in certain locales wave at everybody, others don't. I always found the "universal wave" thing kind of charming and respected it.
I'm a waver on a motorcycle: more of a salute, I guess: left humerus horizontal to the ground, ulna/radius vertical with a palm-forward clenched fist. Fortunately it's never been interpreted as more than a friendly display of unity and solidarity. Some passing riders seem to be kind of taken back by it after offering the usual "low wave" and expecting one back.