USA, New York Seal, Image by StuE, Found by Grant.
Found in Scotland, 20 x 17mm, 6.6g.
Sub-rectangular, bulla-type seal that appears to have channels at the top and bottom for attachment cords. Stamped along these are NEW YOR(K) on one side and U.S. on the other. There may be further writing but it cannot be deciphered.
The style of these seals are reminiscent of British Post Office, square, letter sack seals.
This probably is a US postal seal, see BSG.BS.02089.