The Legion of Merit was an award granted by the United States military in the 20th and 21st century. It was also awarded by the Starfleet Ground Attack Marines.
General Rex Denning displayed the Legion of Merit on his uniform when interrogating the aliens that had crash landed in Roswell, New Mexico in 1947. (DS9 episode: "Little Green Men")
Gunnery Sergeant Ashobi Karuna had earned the Legion of Merit for his service on Torgu-Va in the 24th century. (TNG novel: The Forgotten War)