The plaque is left of the main gate at the Ecole de Gendarmerie de Chaumont, located on the outside of the building.

A large brass inscribed plaque attached to the front of the house.

The plaque remembers the location of the American Expeditionary Force (AEF) Headquarters during WW1.

The site is manged by the American Battle Monuments Commission (ABMC).  From the ABMC website:

The World War I Chaumont Marker is a bronze plaque located at the entrance to Damremont Barracks in Chaumont, France. It signifies the location of the general headquarters of the American Expeditionary Forces (AEF) of World War I commanded by General John J. Pershing.

From the WW1 Commission Website:

Hello Girls in WW1: During World War One, nearly all switchboard operators in the United States were women. Yet when the American Expeditionary Forces deployed to France, they used male personnel to staff these vital parts of the telephone network, even though many of these men had never seen a switchboard!

When General Pershing arrived, he knew things had to change. He issued a personal request for a small unit of women to serve as switchboard operators and real-time translators so that French and American officers could coordinate under fire. Over 7,600 women volunteered for the first 100 slots. Eventually, 223 women and 2 men would serve in France in the Signal Corps Telephone Operator Unit (Female) - colloquially known as the "Hello Girls." They were the first unit of women to directly contribute to combat operations in American history. 

 Under the lead of Chief Operator Grace Banker, left for Europe in March 1918. Members of this unit were soon operating telephones in many exchanges of the American Expeditionary Forces in Paris, Chaumont and 75 other places in France. Supporting combat operations in France, the Hello Girls connected over 26 million calls, averaging a speed of just ten seconds. That was six times faster than the men they replaced. Over 30 Hello Girls received individual commendations, and two made the ultimate sacrifice for their country while in Army service. 

Yet they returned home to bad news. Despite serving under commissioned officers, wearing dog tags, rank insignia, and uniforms, swearing the Army Oath, and being subject to courts-martial, the Hello Girls were told they had served as "civilian contractors" instead of soldiers. They were ignored for decades and forgotten by history.

For almost 60 years, the surviving unit members petitioned Congress for the same veterans recognition afforded to their male colleagues and female Army nurses. Finally, in 1977, Congress passed a law paving the way for the Hello Girls, and the WASP pilots from WW2, to be recognized as full veterans of the US Armed Forces. In 2024, the US Senate unanimously passed the Hello Girls Congressional Gold Medal Act, a measure to honor the landmark service of the brave women who served in the Army as telephone operators and connected American and French military forces on the front lines of World War I.

 Source:

US WW1 Commission Webiste

ABMC Website

The inscription in French and English and reads:

 General headquarters of the American Expeditionary Forces in Europe during the World War occupied the building of the Caserne Damremont from September 1, 1917 to July 11, 1919 and from here directed the activities of more than two million American soldiers