What does the hallmark "A" plus a "Star" mean? | Id. 138

by VStairs
(Alameda, CA, USA)

I have two questions:

1. What does the hallmark mean?
2. Can you give me an estimated value?

I have an old gold ring with a hallmark of a raised "A" and a shape of a "Five Pointed Star" within a recessed rectangle. The gold looks to be 18ct. I know most of the history. It was my husband's aunt's ring, given to her by her husband sometime early in the 1900's. I don't know where he got it but originally it had two rubies.