I don't think it is a seal.The raised strip on the back combined with the point on the tab is more suggestive of an attachment of some sort fitted to the back, possibly a pin, clasp, or mounting bar.
BRITISH WAR OF 1812 ERA EXCAVATED BUTTONS. This interesting lot contains 3 Royal Provincials coat size buttons, identified in Albert's book as LC-1 on Emilio cards. / 1 Cuff Royal Canadian Volunteers,
I think it has something to do with the Transport Board - probably from the c. 1794-1817 era. And might have been used to seal a shipment of items. This board also regulated mail to convicts/POWs and I guess it is possible it could have sealed parcels of mail to show they had been inspected. Just guesses - very neat find!