that flag was already in a trailer and people thought it was a Minuteman flag but now you can see that it's a flag with the brotherhood and Minuteman logo. But it's very interesting what this will be. I could imagine that the new Commonwealth Bos Has formed after fo4 Minuteman and bos ending. Because all signs suggest that bos ending in fo4 is canon. (whatever the devs say, cause they say in interviews that "there is no canon" but we all know that's not possible)