Very nice indeed.
I'm seeing 'S' and 'N' superimposed on one another, with both letters back to front. That would be because it's a 'seal ring' for letters and other documents, such that the letters would appear the correct way round on the sealing wax impression.
The crown (strictly coronet) type is for nobility, rather than royalty. So, something in the territory of Baron or Count if it were from Eastern Europe (no reason to believe it isn't). It's obviously pretty old and may be a one-off that you'll never find a match for, although you may find similar styles. If there's any family history attached to it, that may be your best prospect for dating it.