H500,haven`t a clue,as it was over 20 yrs ago,when I was `freelancing` in a J`box,doing `joy-rides` at fairs,airshows etc,.It may have just been `Company Ops `manual advice for pax.safety,sensible precations,etc...
I know the `ground-crew`/assistants would `tape-off` the area wherever possible,for pax loading/unloading.in case a` jobsworth` was around or a CAA Inspector...