PAT.APF FOR?! Silver locket mystery

Hello magpies! Anyone any idea what this hallmark means, or how old this locket might be please? Not the original chain.
It says ‘Solid Silver PAT.APF FOR on the back. Google is coming up empty on this one! Hoping the genius hive mind (you) can help. Thanks as always! :pray::blush::sparkles:

No hallmark there - it’s just says that a patent has been applied for with nothing to distinguish the maker or the grade of silver.


Thanks so much for the reply! It says SOLID SILVER above the PAT APF FOR. Does that not mean it’s solid silver? :thinking: Thanks!

It certainly claims to be solid silver but doesn’t have any fineness such as 925, 800, sterling, etc. which is what I meant by “grade”.