212 has a point, if the helicopter turned 90° to the left and maintained the deck position in relation to the aiming circle, the tail would be compromised in the 150° sector. By landing correctly each time it becomes second nature especially at night with a side on landing with the tail towards the 150° sector.
The H is an important indicator as it is set up to indicate the 150° sector, plus there is no excuse not to know the landing details as all rigs/vessels certainly in Europe have drawings and mobiles give wind and ships heading so the crew are fully aware of their landing direction in relation to obstacles.
That said I introduced an Helideck test into a training exercise and it was met with blank stares so the lack of knowledge regarding helidecks is I believe widespread. The fault lies both with the pilot, for the information is available, and the training departments for not ensuring all crews are familiar with the deck markings.