Featured Soviet brooch, signed, please help!

Good evening,
This brooch is a new acquisition, bought it in an antique market.
Sold as sterling silver, at the back has a signature, possible Russian alphabet.
It’s very well made, the lady whom sold it, tested it and they are not diamonds.
I have to clean it and post few more photos tomorrow.
Any idea what it is, possible maker?
How old?
Thank you.
Kind regards,
Simona

 

Maybe this word is "Стерлинг" STERLING

 

Possible, it’s not clear, will clean it tomorrow, see what comes up.

 

Simona, would you show a picture of the back and the mark after you clean it?

 

Yes, here it is. The word ends in N and there are some other hallmarks as well.

 

Thank you, Simona. Unfortunately I can't make out the lettering. The letters you drew are clearer. So, I have to think that Aznathalie's interpretation is the most likely.