Oseney

Oseney Abbey's seal is from c.1290, and has the BVM and Child, she crowned (fleur-de-lis); he nimbed (cruciform).  She seems to be giving him a dummy; Birch says it's an orb (could it be a rose?).  Is Christ receiving the nice ball from mama, or is his r-h in benediction? 

Cf the amazing Clare Chasuble (below, courtesy of the V&A); you can read more about it here and on this nice post about Opus Anglicanum.  It's from about the same time, celebrating the marriage of Margaret de Clare and Edmund, nephew of Henry III.  (They were married in 1272 and divorced in 1294.)

(My money's on Bogo de Clare for commissioning the chasuble - Lars Kjaer's exploration of his household accounts show that's exactly the sort of thing he'd go for!  By the way, notice the BVM's seat - very like the Merton one.)
 

On the Oseney seal, Mother and Child sit in a trefoiled arch, with lovely crockets (the things that look like snails crawling up a spire), with buttresses and pinnacles.  Birch notes the inscription De Oxonia on the plinth of the niche.  They are on top of a platform with two architectural corbels, all being a canopy for an ox passant guardant, for Oxford.  The presence of the ox is interesting; Oseney was a major landlord in Oxford, but also had more to do with its university than is generally acknowledged.

The seal has certain similarities with Bruton's, which itself has similarities with Merton's.