I have done some research on these marks and would like to add to the discussion. First, I show the marks from Postnikova of the Assay mark for Mickail Borovshchikov. Notice that there is no dot between the initials.

Second, are possible St. George city marks for the time period.

Third, only one silversmith working in Russia the same time as Mickail Borovshchikov 1755-1768. Semion Semiginovski, a master in Kiev from 1750-1787. He made church items, drinking cups and used the hammer technique for patterns.

I realize Kiev to Moscow is a long distance. But Semion Semiginovski did not have assayers working in Kiev for most of his career. The first Kiev assayer is listed as 1787. Perhaps more discussion of authenticity is needed.
