200822 Vessels exhibiting confusing lights

This is an observation and query concerning the lights exhibited by a passing ship. In addition to the normal lights for a power driven vessel a passing container ship was showing a flashing red light at the masthead. Is it normal for such vessels to show these lights these days and what does it mean? Is it a warning that the ship is carrying dangerous goods, which I expect all container ships do, or is it for low flying aircraft? Or is it a signal for a particular port that they did not turn off? Thanks for any clarification.

Editor’s note: The last reason is the most likely. In many regions, local regulations require vessels carrying dangerous cargoes to exhibit a flashing red light. In Japanese waters, ‘huge’ vessels (more than 200m long) are required to exhibit a flashing green light. To avoid potential confusion outside port areas, and in the good practice of seamanship, bridge teams should ensure that these port specific lights are extinguished before leaving port.