The Guard, Tomb of the Unknown Soldier, Identification Badge is a military badge

Military badges of the United States

Military badges of the United States are awards authorized by the United States armed forces that signify rating, qualification, or accomplishment in several career fields, and also serve as identification devices for personnel occupying certain assignments. Personal recognition is granted to...

 of the United States Army

United States Army

The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...

 which honors those select few soldiers who have been chosen to serve as members of the Honor Guard at the Tomb of the Unknown Soldier

Tomb of the Unknowns

The Tomb of the Unknowns is a monument dedicated to American service members who have died without their remains being identified. It is located in Arlington National Cemetery in the United States...

. It is the second-least awarded badge in the US Army, after the Astronaut Badge

Astronaut Badge

The Astronaut Badge is a badge of the United States, awarded to military and civilian pilots who have completed training and performed a successful spaceflight...

. , only 578 soldiers have been awarded this badge.
The badge itself is made of heavy sterling silver

Sterling silver

Sterling silver is an alloy of silver containing 92.5% by mass of silver and 7.5% by mass of other metals, usually copper. The sterling silver standard has a minimum millesimal fineness of 925....

 approximately two inches in diameter.