Cloth Seal, Bale Seal?, James I, Alnage, Stuart Arms, Image & Found by Jason Sandy.
Found on Thames foreshore near Swan Lane between London Bridge and Cannon Street Bridge, 23mm.
Stuart Arms I R to sides // P inscription around: Mark (bird?) COM ... (M?).
Unusual one disc alnage seal. IR to sides of Stuart arms suggests James. Could be I or II but this style was particularly common in the reign of James I. Unfortunately the county name after COM is missing but if it is an M at the end then EBORVM would fit(see below). Another letter M? seems to be over-stamped bottom right.
Gary Bankhead has found another example of this seal that clearly shows the county name to be EBORVM (B 1071 Bankhead forthcoming publication).