Isn’t the two-finger wave supposed to go along with the two-wheels, as in “Hey, we have something in common. We ride a two-wheeled vehicle instead of the 4-wheelers everyone else around us is driving”. At least that’s what I read when I was trying to figure this all out. Of course there’s “The Californian” wave, as shown in the BBM article “Motorcycle Hand Signals”. It’s pretty cool, but not for beginners.