Thanks you for your reply. I think it's going to be pretty hard to find out. It is a good thinking track that these are owner marks. Was this done often? Why did they place the same marks double?
Here is a link to the item. https://i.postimg.cc/sX6BZL4d/Reliekhoofd1.jpg (admin edit) There is a very similar example of the same workshop in an important Foundation in Switserland. That one has no markings. Object is vetted by different experts and they all agree on the age, 13th -14th century. T...