Here in Milwaukee the HD riders tend to be snobs unless they are in the 45 years plus range. Then they get dreamy eyes remembering when they were 18 years old on their first bike.
I used to wave to everyone on 2 wheels, HD, sport bikes, even mopeds.
Now I tend to ignore HD's unless they nod first, then the nod is returned. Most of those guys are snobs and as another member pointed out, they are "swipe cool" going through a mid life crisis.
I find the sports bike crown is 50-50. I'll get half the ignore me due to thinking I'm on a Harley, or just don't know proper educate. What's really cool is when you get a group of 20-30 of them all with their arms extended. I think it more then makes up to the others.
Mopeds & scooters get my wave no matter what. Most of then give ma a confused look that is worth it every time. I do get the occasional wave back, normally followed by a puffed out chest.
As for the wave itself, mostly a nod followed by a fully extended arm. Although it may look like I am turning left to anyone behind me.
A final note (wow this post is getting long). I was riding around a bend and a cop on a Harley was riding towards me. He put his arm out and just as I was about to return the wave he pulled his arm in an snapped his head the other way. It was as to say, sorry, I though you were on a Harley. LOL