Unfortunately, the marks appear to be faked and over-struck on genuine marks (red arrow).
St Petersburg city mark must not look like this, maker`s mark is poorly cut.
Assayer is missing. Even with limited space on jewelry legislation was strictly obeyed in regard of marks.
Hollow gold and silver was marked on back plate before assembling the piece, every link on e.g. bracelets.
Compare with the brooch I posted.viewtopic.php?f=15&t=46715In a word, it`s not Imperial Russian jewelry.
Let`s wait what other members of the forum have to say.