At the risk of starting something I really don't want to; when you say proof then what do you mean? Ideally I'd be looking for something that isn't just some random person on the internet spotting a mis-grip of a handshake or similar and then determining it as part of an arcane ritual but I appreciate that might be all the evidence there is to support this.
Proofs as in, the same (or very similar) ancient egyptian type rituals present in recent ceremonies in front of our very eyes but which ppl are unaware off or simply ignore as something with no relevance. Societies like the skull and bones, rituals such as those that take place at bohemian grove.
You are right though, we don't want to start something off on here, it's best to just read around yourself and make up your own mind.