Can you tell me please what hallmark (country) this is?

by Marga
(The Netherlands, Helmond)

I bought two pieces of antique jewelry which I think very beautiful.

One round brooch and one little brooch with a little hidden place. Perhaps for some hair or something else?

The two pieces have together three hallmarks.
On the round brooch two and on the little brooch only is: Brevete S.G.D.G.

Are the two pieces belonging together?
Is this blue glass or blue enamel?
And what does the hallmarks means?

You would help me a lot with your answers. Thanks in advance.

M.Dobma