Hello, two crossed hammers for Anton Bahner jun. from the famous Duesseldorf Bahner-family.
A detailed history of that family and its various silverware and flatware companies can be found here
https://books.google.de/books/about/Sil ... edir_esc=y
C. Doerts is Carl Doerts from Dortmund. He died in 1868, but left widow and three kids, obviously the shop (he was a gold- and silversmith) existed after his death. Not sure whether the "900" is not actually an incomplete "800", 900 in that time would be very unusual. Regards Bahner