This way of hand shaking is also a known defensive tactic called a skeletal lock. It aligns your knuckles preventing your hand from being crushed by someone trying to dominate you. Try it, it really works. Just extend your index finger when someone shakes your hand.

I know you are right, that it is also a masonic handshake. My husband was a defensive tactics instructor and uses this handshake. He was once asked ''What lodge do you belong to?" He didn't know what they meant. They then said ''Aren't you a mason?' He is not.