I've perfected the "always grinning face" which works perfectly. It works so good that the players even screw themselves when they make a decision based on my smirk. Whenever they are discussing a situation among themselves, just smile. And always roll dice. I make it a habit to roll dice as often as a person might fidget. It has become my way of fidgeting. That way, they never know when I'm rolling for real, or rolling secretly.
The grinning thing is pretty funny though. It cracks me up when all the players turn just to look at my face to see if I give a reaction. My wife is the funniest about it. As long as they've known me, they still think that my smile means something and she'll be the one to look and say, "Look, he's smiling so he knows we are right!" That just makes me laugh and smile more. Even if they are right, I'll be sarcastic and say, "Go ahead. See what happens." Then I smile even more when they start doubting themselves, "Hmm, now he's trying to trick us."