At the east corner of the building, this is a brass bolt stamped "BM 121 D" and "GSC". The bolt is low on the foundation, of the northeast wall, directly below the stone quoins on the east corner of the building, about one foot above the sidewalk.
Strangely, it doesn't appear in the NRCAN database but it does at Mascot. Its GCM number at Mascot is 490698.
Sit. Fernie Post Office. Front wall, in N.E. face of corner stone at easterly corner, fourth course below water-table.
Geod. S. OF C. precise levelling bolt set horizontally
National Geodetic Data Base description follows.
Fernie
Old post office building, bolt in front wall, in northeast face of corner stone at easterly corner, fourth course below water table.
From Geo BC Mascot