WG DD Caseback Hallmark?

[CHRONOLEX]

Hi all - do you have any thoughts on the meaning or significance of this hallmark or engraving in the center of my WG DD caseback? It's been there since I first removed the sticker. I was hoping David (crowncollection) or others with specific hallmark knowledge may have an idea. Thanks so much!

P.S. Please note this is not my picture. It was first posted by someone else but my engraving is identical. At that time, he and I were both looking for information about it. Thanks again for reading.