Hi, welcome to the forum. I believe it could be a Dutch duty/tax mark.
The Boars head or the 1831 duty mark, this mark is of two sizes. It did not give any guarantee on precious metal content. It has been used as a duty mark on metal with a gold or silver content of 250 minimum. This mark was destined for all imported, unmarked and invalid marked objects of foreign, national and unknown origin. The big sized Boars head used 1831-1855 and the small Boars head used 1831-1893