Image courtesy of eMedals.com
Dmitri Osipov was a Russian jeweller and goldsmith based out of St. Petersburg, who created pieces for the House of Faberge along with many orders and decorations.
Osipov was a joint owner of the ARND. Jewelry Company with Johann Hellwing Arnd from 1890-1900. He then owned the company outright from 1902 until selling to Andrei Karlovich (A.K. Adler).
The markers mark stamp is “AO” (“DO” in Cyrillic).