Marines who label themselves modern-day heathens and wish to mark their grave with Thor’s hammer — their religion’s version of a cross or Star of David — now have Veterans Affairs approval to do so. While some only know of Thor as a comic book hero, he actually dates back to Norse mythology. Thor used his magical hammer to protect humans and other gods from giants. But today, that hammer means something special to those who practice Ásatrú and worship the Norse Gods. And as NPR’s “The World” reported last week, those who identify as such and served in the…