The crossed rifles on Master Sergeant Mark's "Devil Dog" (a popular nickname for Marines) tattoo are not necessarily a mistake. It is true that Marines do not have different branches (medical, infantry, engineers etc.) and therefore do not wear branch insignia. However a number of Marine Corps enlisted ranks (Lance Corporal, Corporal, Sergeant, Staff Sergeant, Gunnery Sergeant and Master Sergeant) have crossed rifles under the insignia chevrons to indicate that Marines at the pay grade of E-3 and above are first and foremost trained, experienced rifleman, which is why the ranks of Private and Private First Class do not use the crossed rifles. There are also a few higher non-commissioned officer ranks that have specific specialties and use other symbols: First Sergeants have a diamond in the center of their rank insignia, also called a lozenge, to indicate their role as a supervisor and leader of lower ranking enlisted Marines. Master Gunnery Sergeants have an exploding bomb cluster to indicate they specialize in the use and maintenance of weaponry and explosive ordinance. Sergeant Majors have a star to indicate their role as a leader of all the lower NCO and enlisted ranks and in recognition of the many years of hard work it takes to achieve such a high rank.
