Ooooo, secrets - how exciting. It's just so obvious that the people doing this need to be special somewhow. The result is silly and immature.

Standard with fraternities, usually consisting of a series of grasps and possibly phrases that alternate between the initiator and receiver. Its purpose it to carry on tradition, and a way of proving membership to brothers who have not yet met you.

My father and uncles had a family handshake and whistle for years, now my brother and my son and I use it. It's not really a secret but it is ours.