The initials TEW probably relate to the ownership of the mortar. A similar scratch mark W was used on a bell (the 5th at Furneu Pelham, Hert's, by Miles Graye I of Colchester, dated 1618). Graye also signed the marriage register and his will with a similar sign-manual W, (Ex.inf. R.P. Butler).
A mortar in the Wellcome Collection at the Science Museum (A.604206) has a similar scratch mark.