Hallmark on Deco Ballerina Band?

[pokerface]

Kind of hard to see, but the hallmark is a diamond shape, and then "OF A".

I assume it means diamond of...something? Any ideas? I bought the ring at a jewelry fair, and was told it was a Deco-era piece.

 

[kgizo]

Did you check Lang’s database: https://www.langantiques.com/university/makers-marks-2/

It’s a great find and I love it with your ER.

 

[pokerface]

I did check Lang’s, but no luck.

 

[Niel]

I am not sure they have the era right but it’s lovely none the less

 

[stracci2000]

I agree with @Niel .
I think it's Mid century, 1950s-60s.
Very pretty! It's a guard ring. There would have been two rings to encircle a solitaire.