Shoulder patch

A shoulder sleeve insignia (often abbreviated SSI), is an embroidered patch used by major formations of the United States Army. Each formation has a unique formation patch, and the U.S. Army is unique among the U.S. Armed Forces in that all soldiers are required to wear the patch of their headquarters as part of their military uniforms.

Shoulder sleeve insignia receive their name from the fact that they are most commonly worn on the upper left shoulders of all U.S. Army uniforms, though they can be placed on other locations, notably a combat helmet. Shoulder sleeve insignia worn on the upper right shoulders on Army uniforms denote former wartime service. These "combat patches" are worn on the Army Combat Uniform but are not worn on the Army Service Uniform. Instead a 2 inch metal replica is worn on the right breast pocket and is officially known as the Combat Service Identification Badge.

Shoulder sleeve insignia were often designed with intricate designs including bright colors, when created. Because these bright colors and designs risk standing out when a soldier is in combat or in hiding, the shoulder sleeve insignia in its color form was commonly only worn on the dress uniform, when a soldier is not in combat. However, with the retirement of the Army Green Uniform in 2015, the full-color SSI has been replaced with a CSIB instead. For combat uniforms, "subdued" versions have been created for wear on the battlefield.

"Full color" SSI were only worn on the green "Class A" uniform. Formerly, full color SSI were also worn on the "full color" (white letters on black or dark blue material) Military Police brassard, worn by MPs while wearing the green "Class A" service uniform or while wearing subdued field uniforms (BDU or DCU) in a garrison environment. However, with the ACU, the MP brassard was replaced by a rectangular patch made of fabric or infrared-reflective material, reading "MP".

The subdued version of the SSI created for the Battle Dress Uniform (BDU) features patches that are primarily olive, dark brown and black, to match the BDU. In general, this version is obsolete because the Army phased out the BDU in favor of the Army Combat Uniform (ACU). A few examples still remain, as older accessories, such as BDU winter weather jackets and coats are still in use by some units, such as ROTC formations. These jackets still use the subdued BDU SSI.

...
Wikipedia