I see as hallmark a building with a flag.
I see the civic arms of Garz (Rügen) a building with a flag.
There are some people with name Burmeister.
I have some hallmarks of Bergen (Rügen) with a very similar 12-Lot mark.
There was a Goldsmith
Chr. Gansen in adressbook 1866,71,74
It is possible, that there was a son H.F. Gansen?