The stamp of master Kenig Otto - Leningrad - initials "OK".
Similar hallmarks
Moscow City Clay 1780 Georgia Pobedonosc
MRClaymo Master Roloves Mattias - Riga - initials MR - 1555-1574.
AKClaymo Master Kirkkenen Arvid Anton - Leningrad - AK initials
CFNClaymo of unknown master Tartu - initials of CFN - 17th century
Claymo of the Palace - Moscow - The Two Eagle - 18th century
Moscow City Clay 1815, Georgie Windows.