I nod or wave to all and sundry on powered two wheels - I especially like waving to scooter riders : I'm sure I detect surprise, shock, puzzlement on their faces/body language when I do, sometimes. A few weeks ago on the strom I waved to some BMW adventure types parked up consulting their GPS's. When none of the group of 12 returned owt I slowed to a stop and waved again from across the road several yards away: they just stared blankly at me and the missus. Eventually I just gave them the finger and rode off! I find it hard to believe they don't understand/have not observed this form of recognition about bikers - they're just snobs. Anyway, some riders don't respond cos they're in difficult decision-making time coming up to a bend or whatever. that's OK (but a part of me still wonders ..'wanker?'
