All being old hands, we all had definite opinions on this particular mark and would not be easily swayed to anothers' opinion!
It was close to the coastline and marking out a hazard of rocks near to a 'current powered' electrical generator tower installed in the channel. Because of the limited space, and without a very close scrutiny, this mark could be interpreted in several different ways.
When you have decided which mark it is you are looking at, you then have to determine where the hazard is, or alternatively, where the safe water is.
This is easily remembered by whichever mark it is, the safe water is outside of it - e.g. North - water to the North is safe, East - water to the East is safe, South - water to the South is safe and West - water to the West is safe.
Waterproofed cards showing this bouyage system are generally available from any recognised chandlery.
Keep one on board at all times posted to a bulkhead by your navigation area.
You can read more about buoys and bouyage systems in my ebook 'Voyage of the Little Ship 'Tere Moana', downloadable from my website http://www.sailboat2adventure.com