I recently came across a mention of what is probably the predecessor of this boundary marker, from five years before this one was erected.
It's on lines 9 to 11 in the following advert for the 8th or 9th sale of land on the Harringay Park Estate. It's referred to as a starting point for a footpath between the Queen's Head and Hornsey Station.
Morning Post (London), 28th January 1882
The 1869 Ordnance Survey map below shows both the marker location and the footpath.