There has been a recent case here at a local pub where the landlord put a square of concrete down for visiting helicopters to land. The council tried to get him to remove it but had to climb down when a planning consultant friend of mine pointed out to them that a square of concrete was just a square of concrete and the small hole in the middle was for putting the rotary clothes line in when required. It is still there but not used very much by helicopters as it is not a particularly nice pub!
If you do put concrete down, probably better not to put H on it. Then you say it is anything you can think of if the council man comes round. If you leave it grass you can always lay a temporary flat wooden H if you are expecting visitors. Easier to mow as well.
Most of the private sites round here are just a flat grass area with no marks other than maybe a windsock nearby. You will find that word quickly spreads if your pub is any good and you can always tell visitors where to land when they phone for PPR.