Whose signature?

[Konstantin]

Here's another opportunity to exercise in erudition.
I was sent a letter to identify the author's signature.
Spread. Theoretically, you can ask for a better photograph if needed.
Presumably Europe.

We only know that this is the second half of the 19 century. At least with high probability it can be asserted. If you look closely, the sign is visible figure is similar to the 52. This is likely a year.