Members of the United States Marine Corps must follow strict rules about when to wear their covers (hats). These include on-base and off-base regulations, as well as issues about saluting officers and the U.S. flag. Uniform regulations change periodically, but the tradition of not wearing covers indoors continues.
In 2005, over 10 changes were made to Marine uniform regulations in a Marine Administrative Message. One change mandated that on a military installation, Marines are to remove all hats (both military and civilian) while indoors. This was a traditional behavior by the Marines, but the Marine Corps Uniform Board had now finally added it to the official regulations.
The exceptions to this rule are that Marines must wear covers if they are under arms (on duty), or if a superior instructs them to do so. "Under arms" literally means carrying a weapon, although an on-duty Marine in an authority or ceremonial capacity may wear a duty belt instead, as a symbol of being on duty without carrying a gun.
Marines are officially part of the U.S. Navy, although they operate as a separate branch of the military. They do not wear covers indoors because they follow Naval traditions when it comes to covers and saluting, as does the U.S. Coast Guard. This means that, like Naval personnel, Marines never salute unless wearing a cover, and thus almost all Marines do not salute when they are indoors. They also are not supposed to salute the flag unless wearing a cover. In contrast, members of the U.S. Army and the U.S. Air Force give salutes even when not wearing covers, but saluting indoors is prohibited except in a formal report to a superior or during a ceremony.
Before the mid-1990s, Marines were not allowed to wear hats indoors anywhere, including off base. Then the rules were changed so Marines could wear hats inside, but not at at a military installation. Marines cannot wear bandannas or do-rags anywhere at any time.
Other changes and clarifications have been made since 2005. Marines no longer must wear their covers in privately owned vehicles. Additionally, they are now allowed to wear motorcycle safety jackets over the uniform while riding. Female Marines previously could only wear pearl earrings with their evening dress uniforms, but in 2007 the rule was changed to also allow diamond-studded earrings. Also in 2007, sleeve tattoos (tattoos that nearly cover a person's entire arm or leg) were prohibited except for Marines who already had them being grandfathered in. This prohibition includes half-sleeve and quarter-sleeve tattoos if they can be seen when the Marine wears standard physical-training gear.