Unable to solve Makers mark on ring (Double "B" with "square"??)

[dapnet921]

I have a 40-50 yr old ring, that has the following makers mark.
Within a circle, there is a capital "B", with what appears to be a "square" that shares
the left line of the top of the "B".
It's difficult to be really certain what the "square" really is.. hopefully, someone
has seen this before.
I have included 2 photos, and 1 photo of a sketch I made.
don't know if its' meaningful, but the left-half of the circle is very pronounced,
the left side is almost invisible.. wear?
Thanks!

 

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