Guano, Tana, Image & Found by FergalThang.
Found in Scotland, 18mm.
TANA straight across the centre, A GUANO... curved around border // triangle bisecting letter S with its base
Antananarivo is the capital of Madagascar and often called Tana. There is a company trading in Madagascan bat guano called Guanomad although it seems rather recent and no evidence of earlier guano trading has yet been found for Madagascar.