Rather off topic, but someone might know...
I'm familiar with a large "H", usually inside a circle, painted on the ground, to signify a helicopter landing pad.
But what is the significance of this symbol, about three feet in diameter, on the deck of a passenger ferry boat? I saw one today: three-foot diameter solid yellow disc painted on the red-brown deck, with "H" in deck colour inside, almost filling the disc. Given that this was a small inter-island passenger ferry in the Orkneys, that the circle was only three feet in diameter and that it was right next to the side of the boat, I imagine that it wasn't for landing a mini-helicopter :-) So what *was* it there for? I'm intrigued.