Old Sarum has a high-viz requirement however it's not enforced with any great vigor even with home based pilots and not at all with visiting aircrew. It is enforced on non-pilot enthusiasts who wander about with cameras.
There is some justification to the high-viz thinking in that ground staff and ATS are able to quickly spot any potential prop kill member of the public wandering about without a care in the world. Old Sarum is perhaps not unique in the airfield boundary and movement areas are entirely open access.