Hi, and welcome to the forum. It looks like an impression made by someone with a tool, loosely included in a class called "countermarks". People have been making marks on coins since there have been coins to mark. Some are simple initials (letters) or entire messages, adverts or pictures. I have a catalog of countermarks as thick as a phone book but most are older than the 40's and yours isn't familiar to me.
This one looks incomplete or made with some random item. As my learned friends have pointed out, it's post-mint damage (
PMD).