Cameo Brooch Hallmarks, EJCY & CO.?

by Crystal
(Brisbane, Australia)

I have inherited a shell cameo brooch from my Grandmother. I have no idea of its history, but as the 375 mark has no decimal point in front, I will assume its post 1975. The other marks read:

EJCY & Co
Then four stamps:
Crown
375
Anchor sideways (maybe?)
A in capital italics (maybe?)
Does anyone know where this came from and when it was made?
She lived in Sydney, Australia, in 1975.
Kind regards, Crystal.