We are once again in danger of being a trifle EURO/US - centric in our views. Anyone who has lived offshore with their machine for any length of time will tell you that the key thing about deck markings is to understand why they are there and how to use them when you need to know how much room you have to play with when manoeuvring on the deck.
I have observed that there are many who operate safely without the slightest idea what that yellow/white aiming circle means. Sad but true because that lack of knowledge may one day cost you dear.
When operating a machine on a minimum sized deck for that size of helicopter the pilot can only be sure he can move the tail into the 150 deg. obstacle sector safely if his bum is kept over the aiming circle whilst keeping the centreline of the helicopter through the centre of the circle. Why would he want to do that? If you have to ask that question you have lived a sheltered life or not been in the business long enough. ;-)
Outside Europe/US there are parts of the world where they have no idea what you are talking about when you ask them how to use the deck markings correctly.
Having said all that those that operate to/from decks built for larger types are not really involved in the same debate but it still helps to know why the circle is there and how to use it when you need to.
G.