The Punisher's skull first became noticeably visible as a symbol during the Iraq War by US military personnel. Service members would use the skull as an unofficial service patch or paint it on equipment. This was most notably done by Navy SEALs of SEAL Team 3 during the Second Battle of Fallujah in 2004. Chris Kyle popularized the usage in his autobiography, later filmed as "American Sniper": "We spray-painted it on our Hummers and body armor, and our helmets and all our guns. We spray-painted it on every building or wall we could, We wanted people to know, We're here and we want to fuck with you."