I've been saved as R on more than one occasion by a wing - often the backside wing - signaling and saying back.
I can understand saying 'Back!'. That would help, but it's not a mechanic in our association.
It happens at least once a year where I've punched back, and the R comes up with a whistle. We look very, very poor as a crew when that happens.
We can't treat that as an inadvertent whistle either - that just compounds the error. Do you tell the defensive coach who got 'screwed' by not being able to pick up a fumble that not only don't they get that turnover, the offense gets another play? So, the whistle overrules the punch back.
Similarly, when a fumble occurs do we signal the other officials that we saw a fumble? No. We throw a bean bag that they might or might not see, then we silently watch the play. This is the most common time for an inadvertent whistle. One official sees the ball carrier go down in a pile and fumble right before hitting the ground, another official thinks the player is down and whistles.
If we have a backwards punch for a backwards pass, why not a signal for a fumble?