The signal works perfectly - it can always be given and seen. *If the
human receiving the signal doesn't understand it, that's not the
signal's fault. *If the human can't understand a simple visual signal,
why would anyone suppose they could operate a radio correctly?

Over the years the rudder wag has been used to relay many things.I
once tried to steer a tow plane and got a rudder wag (meaning NO, I
will deliver you where I know the best lift can be found). For many
years, the rudder wag was used to indicate "Get off now dummy, you're
in a thermal". These little memories never go away, they are always
there hiding in little dusty corners of our minds. If you have left
the spoilers unlocked, the tow won't be going well. You know something
is wrong...................when you see a rudder wag, your memory can
pump out a bad snap reaction. This is exactly what happened to Joe at
Minden. The tow wasn't going well, he knew something was wrong and
probably suspected the tow planes engine wasn't putting out enough
power. Joe had a radio, but I suspect the battery had gone dead
sometime during the morning pattern tows. After repeatedly calling for
Joe to close his spoilers and just after clearing the wires at the end
of 30, the tow pilot gave the rudder wag. A CFI with thousands of
hours instructing, pulled the plug, turned 180 left and flew into the
wires. This accident should never have happened, but the point is, IT
DID!
How can we prevent it reaccurring?
+ Always do a com-check before every takeoff.
+ Never give the rudder wag below 1000 feet
+ Learn and use the proper signals.
My club is religious about com-checks and the tow pilot won't start
the tow until he gets a Canopy & Spoilers Closed & Locked, slack out,
JJ's ready for takeoff.