I think the further South you go the less you get just due to sheer amount of bikers and yep the "Churchill dog" syndrome.
I do nod at any biker/scooter or wave but the ones I don't see doing it back i just think I never seen what they did. I don't stare at an oncoming biker so might of missed it. If there is a group coming I tend to wave and just leave my hand up for a bit
. The only people i don't wave at in Edinburgh is the parking attendants on their scooters.
The only people i don't expect them from is HOG or old skool patched MCC clubs as they tend to have a snobbish minority in them sadly but i still wave (and get them back from the ones who make the effort).
Uk is nods or a wave very few I see wave a leg
USA you get the peace sign with fingers pointed towards middle of the road
Europe and specifically Germany tends to be a leg wave but both the last two areas they drive on wrong side so easier due to where throttle hand is