In case you have no idea why the punisher is a popular symbol, here's a nice write-up by Eric Milzarski https://www.wearethemighty.com/mighty-culture/why-punisher-skull-beloved-troops/ (Marvel Comics) Frank Castle, better known as The Punisher, is a very deep character. In his first appearance in Amazing Spider-Man #129, he was actually an antagonist pitted against our favorite wall-crawler. He’s hired to kill Spider-Man by a villain seeking revenge for the death of Norman Osborn (known as the Green Goblin by most), which was pinned on Spidey. Castle puts up a good fight, but eventually has a heart-to-heart with Parker. He reveals his frustrations with being a vigilante killer, but it’s something, in his mind, that has to be done sometimes. Many writers have penned fantastic stories for the Punisher since his 1974 debut, but throughout them all, the heart of the character remains the same. He’s a highly-skilled Marine Corps veteran who lost his family to criminals and is forced into taking extra-judiciary measures to ensure the killers can’t strike again. From storyline to storyline, Castle dons his infamous white skull on black gear and puts a bullet into the worst of the worst of the Marvel universe. He’s not a typical hero — he definitely commits countless crimes for the sake of good — but he’s also not a villain. He will go out of his way to not harm the innocent. He’ll gather information on whoever he’s going after to know if they’re really evil, he’ll spare any low-level bad guy who wants to surrender, and (perhaps the most prominent piece of evidence against villainy) he never enjoys killing. He’s comfortable with it, and his mind is at ease knowing someone innocent is safe because of his actions, but he has never been shown, in all of his 45-year-long comic history, enjoying the act of killing. That’s what separates him from the psychotic villains he encounters. It’s his duty to protect the innocent. It’s his burden to have to do terrible things to make it so. That’s something many troops can get behind.