The next difficult bit is to stop the groundcrew approaching even with the light on! Pressure on 20 min t/rounds etc does not help.
We now conduct several turnaround audits a day (and night) using video and a detailed checklist to trap this sort of practice. If we see something seriously dangerous then we will intervene straight away, of course, but we use the audits to bring unsafe practices to the attention of Handling Agent management. This is then fed back through recurrent training, which we also audit. Hopefully this will produce a better long-term safety culture than simply issuing a bo##ocking on the spot.
This is the practical side of having a Safety Management System. It's not just mumbo-jumbo, but it does take time to work through and have benefit.
Do please leave those belly/top lights on until it's completely safe to approach the a/c. I don't think that relying on someone hearing the engines spool down is a good idea at all! The APU noise is quite sufficient to mask this cue.
Cheers,
The Odd One