never heard of this form of acknowledgement in the UK we give a slight nod to the side to show we have seen each other occassionally we'll stop at the same stop point and have a chat about bikes in general and how much trouble there is with living in theUK nowadays and how its driving people out and which has lead me to plan to leave the UK after university. in general its mostly the pure superbioke riders who dont do this as they are only on the road to enjoy riding and not others company aswell.