Silver ring

[BrashkeL]

Hello everyone, I inherited this silver ring, could you help me with the marking?
As I understand this 916 silver ring was made in 1958-1992 period in Soviet union, and the small letter on the left to the star identifies assay office.. decide if it is letter э (stands for Tallin) or в (stands for Krasnoe, Kostromskoy district).
Also, I can't find the symbol which reminds me of Greek letter π and a 9 (?) besides it, can anyone identify this?
What might numbers 27 mean?
Is this Ruby? I guess lab ruby, not mined?
Thank you!

[AG2012]

The stone is most probably spinel, closely resembling ruby. These two gemstones are difficult to distinguish. Until the late 19th century, there was no distinction made between ruby and red spinel, as they look identical and are found in the same localities. Many famous old "rubies" were discovered to be in fact spinel. For example, the enormous Black Prince's Ruby" in the royal crown of England is actually spinel. They have completely different chemical and crystalline composition and different hardness. Rubies have a hardness of 9.0 on the Mohs scale of mineral hardness. Spinel is 7.5—8.0 Mohs scale hardness. Unmounted ruby of this size (I guess about 2 carats) would be extremely expensive (not allowed to tell the exact price due to forum rules).

[Qrt.S]

Actually your almost on the track;-))
Your ring is made in the Estonian Soviet Socialist Republic ESSR. This Cyrillic letter 3­ is called backward E and it stands for "Estonia". The mark you think is a Greek letter is only the letters TJ combined and standing for Tallinnskij Juvelirnij Zavod i.e. Tallinn's Jewellery Factory. Number 9 is the manufacturing year 1969. The figures 27 is probably a model number, journeyman's mark...whatever... The silver fineness is 916/1000.
I cannot say what the stone is. It is very difficult to know that based on a picture only (at least for me not being a gemstone specialist). Let's wait and hope that somebody else can identify the stone.

[BrashkeL]

Thank you, guys! Your answers were very useful! So I guess all is clear with the markings, only the stone remains questionable.
Here are some photos of the stone in a daylight.