My most reliable tell (At least for this session)

[papa_georgio]

I went to Dallas and stayed with my brother in-law, and he invited me to play in a poker game with his friends. There were seven players and I noticed that four of them had the exact same tell. All four of those guys were using card protectors, or putting their cards under some chips. I noticed that If they were bluffing and were prepared to fold to a large bet or if they were limping and hoping to see a cheap flop they would not protect their cards the way they would if they were confident with their hole cards. They would just leave them exposed and not put their chips on them, as if they were already planning on mucking. Unfortunately for my brother in-law he was one of those guys, so I told him after the game because he really is a good player, and he is my brother in-law so I felt it was the right thing to do. I just hope he didn't let any of his friends in on it so that when I go back I can make some more money off of them. Is this a pretty common tell? And has anybody else discovered something like this tell that my go unnoticed, but when you see it, it jumps out at you?