Attribution cross

[U-niks]

Another possible "footprint" - in the history of the Russian Navy are several ships named "Sinop" (battleship, battleship, minelaying boat, etc.). Perhaps the cross was used, for example, when the ship worship?
And some strange thing - not Google or Yandex know the expression "Office of Her Imperial Majesty" (with the exception of the Office of the Empress Maria, wife of Paul I).