I do not know the origins, but the "Shaka" did originate on Maui (I think).
The "shaka" is the thumb extended and the little finger extended ( perhaps that's the letter "Y" in ASL/American Sign Language but I do not know ASL so cannot confirm this).
With the thumb and little finger extended, the "shaka" is a twist of the wrist to wave these two fingers in
a little arc.
Could be an old time surfing sign, but I think it's been pretty much windsurfing related AFAIK!
Hope this helps,