From conversation in the past, on here, leg waving, if I remember correctly, is done by those who ride sports bikes, cos of the riding position; it's easier than nodding. I've seen riders do it, when the vehicle in front moves over to let them past, as a kind of thumbs up
For future ref you may like to use the Random Rant thread?
http://www.bikermatch.co.uk/sites/bm/forum/posts.asp?to...ic_id=1787