S.U Victorian ring maker's mark

What is the item?

Victorian 18ct gold diamond & sapphire ring


Can you please provide all background information?
The year stamp has been worn away through resizing and by finding out who the maker (S.U) I can perhaps narrow down time frame of manufacture.


What are the markings? 18ct, crown, Chester Assay, maker's mark S.U


Where are the markings? inside band