Here is a chess clock from Insa, the famous Serbian clock manufacturer from the Zemun district northwest of Belgrade. To be on the safe side, I would guess that the clock is from the 1970's or 1980's, but it could be earlier. According to the chess-museum.com website, the factory was severely damaged during the bombardment of the city of Belgrade by the US Air Force in the Kosovo War (the website mentions 1986, but as there was no bombardment in 1986 to my knowledge, but only in 1999, I assume the latter was meant). Anyhow, production was resumed after the end of the war and Insa until today produces a variety of clocks including chess clocks.