Can you help David identify this family ring??? Supposedly it has a Dewhurst signature.

This signet ring came from Martha Dewhurst, my great grandmother, passed to my mother and then on to me. It fits my little finger
so was obviously worn by a woman. You can see it is red one side and black the other. That may signify a partnership
with one dead and one alive eg as it did for Rolls Royce - the original badges were both R's red and then one black
and now both black.     

Email David here...