Defensive Signals

[ccbestul]

Did a 4 hour scrimmage yesterday and a question came up with when defensive signal calling becomes illegal.
Sit: A QB had his hands under the center and sent a man in motion. Defense was playing a Monster to the strong side. During the motion, B yells "Roger Roger" (for right) and an offensive lineman jumps. Ref. flags and penalizes B for disrupting QB signals. His rule of thumb is once a quarter back has his hands under the center, any defensive signals that cause A to jump, the penalty is on B. Being a BJ, I'm curious, is the the rule of thumb used by all Referees?