I follow the rule that you wave at everything with 2 or 3 wheels, including scooters. When I was first riding, it made my day to be recognized by other riders, so I try to do the same to the new scooters. The exception for me is at a bike rally or on bike nite....no waving since it gets ridiculous.I read in one of the bike mags, about Australia in particular (and we have folks on this board who will give an authentic answer), that they don't wave, you nod your head. Which is what I already do if caught in the middle of shifting of something and dont have a free hand.