Cloth Seal, Cloth Worker's Personal Seal, Pictorial Device, Anchor & Cock, Image & Found by Derfel.
Found on Thames foreshore, 18 x 25mm.
Bird overlaying anchor // blank
Possibly a rebus using the various terms applied to the type of bird and anchor at the time. There was also an area of the river bank used by dyers covering Anchor Lane and Three Crane Lane and so possibly a dyer's seal.