In the U.S. Marine Corps, the uniform is a symbol of the history of the Corps and a testament to the personal achievements of the individual Marine. Consequently, the proper display of ribbons and medals on the Marine Corps uniform is of the utmost importance.
Consult Marine Corps Order, or MCO, P1020.34G, "Marine Corps Uniform Regulations." This document governs the proper wear and appearance of all Marine Corps Uniforms. In particular, Chapter 5 details which medals and ribbons are authorized for wear and how they must be worn.
Determine whether the occasion calls for full-size medals, miniature medals or ribbons. According to MCO P1020.34G, when wearing the service "A" coat during a social event, the Marine may elect to wear either full-size medals or ribbons. When wearing the evening dress uniform, Marines must wear the miniature medals. When the Marine is wearing the service "A" coat during the regular work day, he must wear ribbons only.
Verify the order of precedence for your ribbons or medals. The order of precedence is located on pg. 5-4 of MCO P1020.34G. The precedence runs from the left to right and top to bottom of the ribbon rack.
Mount ribbons and medals to the mounting rack. The mounting rack consists of two or three long metal bars. The medals and ribbons are designed to slide on and off of those bars.
Pin the rack, with ribbons or medals mounted, to your uniform jacket. For both males and females, the mounting rack must be placed one 1/8 of an inch above marksmanship medals.
Pin marksmanship medals onto the uniform jacket. Marines earn marksmanship medals when they qualify with their rifles. There are three qualification medals available in order of increasing proficiency: Marksman, Sharpshooter and Expert. The marksmanship medal should be placed 1/8 of an inch above the top edge of the left breast pocket.
Attach unit citations ribbons. These are ribbons that are awarded to an entire unit rather than an individual Marine. You are only eligible to receive a unit citation ribbon if you were assigned to the unit at the time that the ribbon was awarded. Center the Unit Citation Ribbon 1/8 of an inch above your jacket's right breast pocket.