All I recall is something along the lines of 'Hurry along' or 'We're about to leave'. I can't recall being told that the hustle alarm means that I can't board.
And that is the problem in a nutshell. Regardless of being told specifically not to board if the hustle alarm is sounding, regardless of the warnings of trying to board when the doors are closing, there is still an insistence of doing whatever you wish and ignoring the warnings. I personally make them regularly and they are made at my TOCs stations and there is a poster campaign.
The doors are in the process of closing, please do not attempt to board, please do not encourage it please highlight to others that you should not board if the doors are closing.
Feel free to go to the RSSB website and search through the research papers regarding passenger behavior when boarding and alighting. A lot of which revolves around promoting good behaviors and discouraging the bad ones. It also includes campaigns to highlight the risks to passengers and help educate. You can also find recommendations made in the final sections of the RAIB reports after a trap and drag.
Trap and Drags are very serious incidents and we should do everything we can to prevent them. Stand clear of the doors, stand behind the yellow line, allow people off before trying to board etc etc are just a few examples of trying to encourage good behaviors are the Platform Train Interface. Encouraging people to block doorways. hold open doors, remove passenger luggage, and justify jamming hands, arms, and boarding when the doors are closing only promotes and encourages behavior that will lead to another trap and drag.
The PTI (platform train interface) is one of the final places that is a serious risk and causes injury to passengers each year. People on this forum are in a fortunate position where the dangers are highlighted and discussed with various sections of the industry. We should all promote good passenger behavior and help drive the risks at the PTI down.