While he was there, Caitlin revealed to Eddie something that she and Bones do when they're around people. Caitlin doesn't like when Bones is on his phone too much when they have company at the house or at dinner. So whenever he is on his phone a lot, she tugs on her ear to let him know he needs to put it away. He in turn also wanted a secret signal for something, so whenever he tugs on his ear then she has to give him an affirmation out loud.
Bones confirmed on The Bobby Bones Show today (February 9) that this is definitely something they do when Eddie shared the new information. He also added that he does get on his phone a little too much so it's a good thing they have signals.