Here in the states, we mostly wave. We nod if for some reason you can't take your hands off the handle bars, like at a stop light, where you have the clutch pulled in. I find that about 80% of riders wave. I don't know why some riders don't wave, maybe they didn't see me, maybe they are beginners, maybe they are on the phone, or maybe they are just snobs. When I first started riding back in the 70's, we waved by raising a closed fist, which stood for motorcycle power, which I thought was a super cool wave. But people don't wave like that any more, probably because it is also the sign of the Black Panthers, so people quit giving the motorcycle power wave. I still use it, since I think it's cool.