It's the middle three fingers. I don't know if it is supposed to be left or right hand, but I use the hand that is nearest the waiter and tap it very casually, 2 to 3 times, as tho I was an old pro.
I've made 8 and 1/2 trips to China. The 1/2 is when I was in Hong Kong for the turnover in '97. When I arrived, it was a British possession, but when I left ---it was China!! LOL!
Wow! I sure wish I was married to a lawyer so I could afford to travel. Preachers are notoriously poverty stricken. LOL. I don't know why I am fascinated by China. I love the people. They seem so gentle and refined (except the Communist leaders).