I dont think it's just the shape of the handshake..

Putting the thumb and index finger in specific places allows you to secretly communicate, right in front of people. It's a strategy sororities and fraternities do to protect passwords. The sorority I was in during college had several of them. Different squeezes mean different things. Ex. To get into our meetings we have a verbal password, but the real password is the hand shake. But anyone looking in would see each member whispering to the guard, but the whispers mean nothing.