Hi Ralf1e,
Your item has the makers mark В.И.И in rectangular cartouche which is the mark of Vasily Ivanov.

Rough translation:
Vasily Ivanovich Ivanov was the owner of a silverware factory founded in 1870. In 1897 his products made him an income of 9000 rubles. His factory was open 1870-1908. He was known for making trays, milk jugs, creamers, napkin rings, cups (such as yours) and silver bottles.
The assayers mark is for Anatoly Artsibashev who worked 1891-1896 in Moscow, which is also the city that the townmark of St George (on your item) represents.
Regards,
Piette