Emphasised to the max in our lesson program.
The only 3 injuries Ive experienced from kiting is from 3 times the launcher let go of my kite before getting the 'Thumbs up"
Once just an ignorant arrogant prix who was too self centred to do the job properly.
The other 2 times I put my hand up to indicate 'hold on a minute' & they took it as a 'thumbs up".
One of those with one line wrapped round the bar - instant death spiral down the beach & into a tree. 2 x broken ribs that time.

Make it a definite eye contact 'thumbs up' above your head. (and dont indicate anything if you are not sorted)
You will find that the ones that launch inappropriately are also the ones who do not give clear signals themselves.
If you want to get the message to spread just keep holding the kite through all the waves & head nods till they are yelling at you. Then stick your thumb up and yell back "Oh do you mean 'thumbs up' Im ready now"
Pysses people off no end - but I reckon ur doing them a favour.