Guano Seals, Damaraland Guano Company, Image & Found by MTC Cocoon Wim.
Found in the Oudenaarde region, East Flanders, Belgium, 40x20mm, 11.9g; 38x25, 10.3g; 35x20, 12.4g.
Click image to enlarge.
(on disc) G.V.M. (on triangle) GUANO across top DAMAR down left side ALAND up right side // (on disc) CONCESSION curved around border (on triangle) BELGIQUE / HOLLANDE / NORD / DE LA / FRANCE (with FRA NCE split at the apex of the upside down triangle)
Note that the front and back of the disc and triangle are independent of each other.
Damaraland "was a name given to the north-central part of what later became Namibia, inhabited by the Damaras. It was bounded roughly by Ovamboland in the north, the Namib Desert in the west, the Kalahari Desert in the east, and Windhoek in the south."
See BSG.BS.01212 for a seal and details of the Damaraland Guano Company Ltd. The seals above appear to be a 'concession' to supply the Damaraland guano to the listed areas of the Continent - Belgium, Holland and North France.
So far we have no explanation for the unusual shape but Euro-plombs shows another triangular seal but with a loop rather than a disc at the top.
From Michel Royer, "G.V.M. probably G & V. Moreels of Gent, (also factory of the superphosphate and were dealers (concessionnaires) for the guano of Peru). Maybe also those of Damarland? The origin of the lead seals would also correspond with Belgium (and North France and Holland)."