Yes, using the standard emergency horn should be banned when its not used in an emergency or for genuine reasons as it gives me such a loud fright (and fears that I'll drop my phone), completely unnecessary and unwelcome when I am filming the train.
I get its the driver being nice but I would rather a nice wave or thumbs up than being blasted by a 90+ decibel horn (made worse in tunnels/under bridges etc were I actually brace for the noise). Guess you can't please everyone