The way that two people who are obviously in love hold hands. It involves slightly tracing each other's palms and gently scratching the other persons palm, looks a bit like your fingers are doing a sort of jelly fish motion. This is usually accompanied by looking into each others eyes and a stupid smile. Most of the time this handshake is done with your hands in the air as apposed to the side (like in traditional hand holding).
It should be noted that if the two people doing the handshake are not in love it looks quite stupid.
Person 1: So, how are things going with you and that guy?
Person 2: Not well. I saw him doing the I Love You Handshake with another girl.