In reply to Pids: A few years ago I was a Trustee on the JMT. I was also a fairly active climber and had been up and down the cliffs of Ben Nevis a few times. I was often happy to see the marker, and actually abbed off it at least once to enable a safe, fast, and low energy descent down the top section of No.4 Gully. (One could, given the right snow conditions, use a snow bollard. Maybe. Sometimes.)
The JMT then purchased a lump of land, including the plateau of Nevis. They decided, rightly in my opinion, to clear much of the human inspired detritus off the bridle track and plateau. Unfortunately, and they said this was done with input from climbing organisations (by which I suppose they meant the MCofS), this included the No. 4 marker. I voiced my protest at this, although, if my memory stands me well enough, it was never brought to a vote by the main committee, it was decided that this clearance would include the marker. I stated that if it were taken down, climbers would simply put it back again. I was met with a shrug of the shoulder, literally.
If it has been removed, as seems to be the case, I am surprised that it would have taken so long for the JMT to do this. I am also surprised, though I may be wrong, that the MCofS have raised no alarms over its removal. Although it is/was an obvious manufactured piece of metal, to me personally it resonated with history, and was always a welcome object.
Surely a few requests for information to both bodies would circumvent most of the postings here, enough to have papered the inside of the CIC Hut a few times over ...