The first part, top row, of the MD-2 (RU: МД-2) fuze's markings is actually 'Z50F' ('Z' Fifty 'F') and not '350F' (Three Five Zero F), in Russian Cyrillic this is 'З50Ф'. This marking covers the factory code, with details below.
So the 'Z' (RU: З) is presumed to be the abbreviation for Factory in Russian, i.e. Zavod (RU: Завод). The 50F part is likely the factory code itself, which is, as far as I'm aware, the Penza Bicycle Plant (RU: Пе́нзенский велосипе́дный за́вод) that is also known and the Frunze Bicycle Plant ZIF (RU: Велосипедный завод имени Фрунзе «ЗИФ»). The code ZIF on fuzes is likely what people are more familiar with.
I'm not sure about the F3 (RU: Ф3) code in the middle, but this is possibly a factory, or other establishment, inspection type code.
On the bottom row the '20' will be the fuze's lot number, whilst the 35g (RU: 35г) is short for 1935 and year (RU: год) in Russian.