Cloth Seal, Cloth Worker's Personal Seal, Privy Mark 
Cloth Seal, Cloth Worker's Personal Seal, Privy Mark, Image by Derfel, Found by Peter Olivant. 
Found on Thames foreshore, ?mm. 
 
Ligatured initials (?I)S // uncertain design - ?privy mark 
 
Most probably a clothworker's personal seal.
 
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