The only image of an overprint I could find was on this 5 Leva of the same (1916) Silver issue.

The stamp on yours certainly looks contemporary (and the hand written number to the right) because it's very faded.
What do they mean? Well we are talking WW1 era and circulation for some years after. Unless you can decipher any wording on the stamp it's just going to be speculation. Perhaps just a bank authentication stamp of the note?

The stamp on yours certainly looks contemporary (and the hand written number to the right) because it's very faded.
What do they mean? Well we are talking WW1 era and circulation for some years after. Unless you can decipher any wording on the stamp it's just going to be speculation. Perhaps just a bank authentication stamp of the note?



















