"Learning the local shaka hand sign (fold first thru ring finger down, stick out thumb and little finger, then pivot it back and forth) as a thank you will endear you to all locals when you pull over, or ask to merge, etc. Just use it sincerely."
To send a shaka: make a fist with either hand. Extend the thumb and pinky while keeping the middle fingers curled under. Face your thumb and pinky away from your body and draw an invisible “j” in the air. Give your shaka a shake and you’re communicating Hawaiian-style!
The shaka is a simple yet powerful way to remind locals and visitors of the way people look out for each other on the islands and strive to spread aloha day in and day out, in keeping with the Hawaiian principle of malama i kekahi i kekahi, - take care of one, take care of all. If you’re new to the islands, don’t be shy about throwing up shakas, just make sure you’ve got the hand gesture down first! Aloha in the Hawaiian language can mean love, hello, goodbye, affection, regards, fondness and compassion. The amazing “shaka” communicates all this and more with just a simple wave of the hand.
Good thing I found this out before going to Hawaii otherwise I might have just signed "bacon" instead.
[hat tip to Trip advisor]