What is the USV on the Roosevelt uniform on night at the museum?

In "Night at the Museum," the USV on Roosevelt's uniform stands for "United States Volunteer." This designation reflects Theodore Roosevelt's historical role as a leader of the Rough Riders during the Spanish-American War, where he commanded a volunteer cavalry regiment. The inclusion of the USV on his uniform serves to highlight his adventurous spirit and commitment to service, aligning with the film's themes of history and heroism.