Cloth Seal, Cloth Worker's Personal Seal, Privy Mark, WM

Cloth Seal, Cloth Worker's Personal Seal, WM, Image & Found by London Mudlark.
Found on the Thames foreshore, 20mm.

Privy mark? P or B Y to sides // WM on rivet head

Looks to be a two disc cloth worker's personal seal although the the mark is unusual. No parallels have yet been found.