Cloth Seal, French, Saint-Omer, Bulla-type, Image & Found by Redgy Dewulf.
Found in maritime Flanders, 22 x 13mm.
Arms of Saint-Omer // partial flower head, arms of Saint-Omer sideways on bottom tab
See BSG.CS.01800 for different example of this unusual type of Saint-Omer cloth seal.
Not a tubular, 'pipe' type seal, see BSG.CS.01818 for a definite Saint-Omer tubular seal. These have more of a clip and tag appearance and are better classed as bulla-type seals, possibly used on goods other than cloth.
The edge shots show a bulla-type seal structure with an extra tab below. Perhaps these seals serve the same function as the tunnel/tubular/pipe cloth seals but with the thread running through just the top section. It still does not explain the deep recess between the two sections.