Also keep in mind that depending on the type of operation PVT or COM, and the "flag state" of the vessel and/or aircraft, you probably will not need it.
Mmmmm!
Maybe this explains why most incidents of helicopters striking objects on or adjacent to helidecks (Onshore or Offshore or on vessels) occur in areas where there are no rules or the rules are so lax (e.g. API in the GOM) that helipad, rig or vessel operators pare down or ignore any regulations that will cost them money or cause them inconvenience!