Hi, It was made in Denmark (first mark on top three towers of Copenhagen,year cannot be deciphered). OM is assay master Cristian Olsen Moeller who worked 1831- 1840. See here: https://www.925-1000.com/dm_Assay.html
Yes the assayer/guardein (uppsidedown M-mark) is Møller but assayers didn't make anything! They were officials guaranteeing the fineness only. I believe the OM mark belongs to the maker and he would be Ole Peter Mønichen 1803-1853 (He made spoons). He was active in Copenhagen 1830-1846. Then he moved to Helsingør and worked there 1846-1853. His widow continued with the business to 1860. The last mark is the zodiac mark and it looks like the lion 22.7-21.8....but....?