Well, the US military has approved of this symbol for the gravestones of US soldiers if they wish it.
Back in 2007, the widow of a soldier requested a pentacle on her dead husband's gravestone as he was a pagan. The military refused because it was a pagan symbol, not a symbol of religious faith. She sued, and got the symbol approved. (Why it was like that, I have no idea. There have been at least two officially recognized "satanic" chaplains, and Asatru and Wicca have been recognized as valid faiths for the past 30 years.) In 2010, the military opened up the process so that other religions could be considered.
Last year, the mother of a Marine who died in combat requested the Thor's hammer symbol for both her son and her husband who had died years earlier. She filled out the paperwork, and ten months later, we have this.
Why do I get the feeling some of the people who will be requesting this are just comic book nuts?
These men, these soldiers, are willing to give their lives to protect our freedoms and help those in other countries. Let 'em put whatever the hell they want on their friggin' tombstones, will ya?