The maker’s mark in a lozenge-shaped reserve either was poorly struck or the punch was damaged, resulting in a point of the lozenge that appears cut off. This slight flaw is not a problem in terms of authenticity.
If you can’t see the maker’s initials or symbol inside the lozenge, then we can’t either. You might check the French Ministry of Culture online database for Paris makers registered after 1878 if you do manage to come up with some initials.http://www2.culture.gouv.fr/public/mist ... 4%24%2534P
Alternatively, as Dunhill is still operating, you might contact the company directly to determine the maker of your case.
Good luck with your research on this item.