My Grandma's Locket

I did some cleaning up around the house and came across a box with my grandma's locket. I polished it a bit, and here it is!

I remember my grandmother (Oma) telling me that she didn't like it because the jeweler made a mistake. He knew her as Hanne, but her full name was Johanne. So when he engraved the locket, he put H S, instead of J S on the back. She felt too embarrassed to tell him and took the locket home.

I am not sure how old it is. My best guess is that it might be from the 1920's. My grandmother's initial for her last name is for her maiden name. I am not sure when she got married but I will try to find out.

The front of the locket has a small ruby. It is overall in good shape but has taken a bit of abuse when I used to wear it as a teenager (I always found big and unusual pieces attractive)

Thanks for looking:)