[grantsrc]

In NCAA this should be killed if the signal is given while the ball is airborn, see AR 6-5-3 VI. If the "poison" or "get away" signal is given while the ball is in the air, opon catch or recovery the ball should be killed. Also, it is important to note that there is no foul for an invalid signal in NCAA. I tell each punt returner prior to the game that any waving of the arms while the ball is in the air I am going to kill. If the poison signal is given while the ball is grounded, the play continues.

In NFHS, I think you made the right call by the book. I personally am not a fan of the invalid fair catch foul. Why have this foul in place? I am sure there is a reason, just not sure what it is. The signal here is given to his teammates and not the opponents. Although the play should certainly be killed once he starts to advance w/ the ball here.