Hi Lissa, welcome to the forum.

It is a Portugese hallmark.
See;
https://www.925-1000.com/foreign_marks6.html
The sitting boar, used from 1887 to 1938. The frame shape, cut-corner square, is for assay office Porto, 1st standard silver 916/000.
Down to the right of the boar, is the unclear maker's mark. Maybe if you clean the maker's mark someone will be able to identify it
Peter.
Source;
World Hallmarks Volume I Europe Hallmark Research Institute 2nd Edition, Whetstone, Niklewicz, Matula. Page 211