Ladies with Rings

[MarcoP]

I was looking at Italian pictures mostly, and thought it was a key, but 


(segretezza overo taciturnita)

only now (researching British literature), i realize it is indeed a ring !

Thank you, David: both images are very interesting (but I have nothing to add about St.Edward).

Cesare Ripa writes that the object is a small key having the shape of a ring ("picciole chiavi antiche fatte a guisa di anello"). 
Here there's a rather long discussion of these ring-shaped keys:
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Ripa also mentions rings used as seals, again with reference to secrecy. 

As we do now, also the ancients used to seal letters with rings worn on the fingers, so that communications were not seen or made public.

"Usavasi ancora dagli Antichi sigillar, come ora, le lettere con anelli, che si portano in dito, acciò che non si vedano, o palesino i negozi"