As a biker, whenever I pass another biker it's customary to nod your head - taking hands off to wave could have disastrous consequences!! It's considered really rude to fail to nod, even if two or three bikes are passing and you end up doing a good impression of a nodding donkey. Unfortunately, some modern scooters look a bit like bikes, and it would be anathema to nod to a scooter rider so you have to wait till the last minute in some cases, just to be sure it is a fellow biker!! Talk about snobbery.... Anyway, when I was being dragged up in Yorkshire, the standard greeting was Eyup! Or even, How's thee laikin??