Actually, validity would be a non-issue here since ANY waving signal would cause the ball to become dead when possessed.
So, what if the on-field officials consciously make the judgment that there was no signal, i.e it was an eye-shading or just a arm movement to maintain balance? If the RO pages, and the R goes to the headset and tells the RO that they ruled no signal on the field, then the RO wants to get involved because he thinks its an egregious error? BS.
Now, if the R says that nobody saw a signal or arm movement any kind when, in fact, there was an obvious, clear signal, well, OK.
Judgment is an issue.