The idea of motorcyclists waving to each other as they pass on the road is something I only came across after I moved to the USA. Back in Britain, motorcyclists are more likely to nod their head as a means of acknowledgement.

The nod has an obvious advantage over the wave in that both of the rider's hands can remain on the handlebar. My father told me that the only time you'd see a British biker take a hand off the handlebar would be to flick the ash off the end of their cigarette. I often see Cruiser riders nervously waving their left hand in a quick, flicking motion to minimise the length of time they are single-handed.

As an aside, I've also noticed that the British biker's nod is predominantly a downward motion of the head, whereas the US equivalent is mostly upward.