The lord marshal top is a reward from the Mobilising Armiesminigame. They cost 185,300 Reward Credits to purchase them from Lord Marshal Brogan on the second floor of the Officer Tower. Only players who have a rank of 300+ can have access to this clothing.
The examine information for this top is a reference to U.S. Marine Rifle Creed that can be found in the movies Full Metal Jacket and Jarhead, which goes: "This is my rifle. There are many like it, but this one is mine."