Just tidying up some blasts from the past (including some very ancient ones), largely for the benefit of anyone searching the site for information.
Interesting find. These odd-shaped porcelain mugs with a flattened profile were specifically made for sipping invigorating and medicinal spring waters in various spa towns and sanatoria in Russia. The mugs could be purchased as souvenirs.
This one is ‘Essentuki’ branded, with the same base mark as yours.
https://www.ebay.co.uk/itm/185476847282
On the body of the mug, yours is marked in Russian for what we call the city of ‘Kislovodsk’. The city name translates as “sour water” in relation to the minerals present in the spring water there, known as ‘narzan’ (translated as ‘drink of the gods’).
Note that, as well as the pottery mark, it has a price mark of ‘1 ruble and 15 kopeks’ (what we call the ruble was written as ‘рубль’ in Russia, so it has a ‘p’ symbol, not an ‘r’ symbol). In the Soviet era, prices for consumer goods were state-controlled and luxury goods were required to be price-marked to prevent profiteering and keep a rein on inflation. I would think the mug is probably from the 1960s or 1970s (and certainly before the dissolution of the Soviet Union in 1991).