This small key is stamped CVRY for Central Vermont Railway on its bow. On the opposite side is stamped S.D. It is in excellent condition, attractive bright brass with light signs of use and no metal damage.
Although the key is 1-3/4 inches long, it has a narrow, 1/8-inch hollow barrel that will accommodate a tiny pin (of about 3/32 inch).
The most common use of the abbreviation "S.D." is Signal Department, but without documentation, it is possible that "SD" may have stood for something else. Although most Signal Department keys are significantly larger and sturdier, it may have been made for an office cabinet, document box or some sort of small utility lock.
The Central Vermont Railway was a New England railroad line that operated in the U.S. states of Vermont, New Hampshire, Connecticut, Massachusetts and New York, as well as the Canadian province of Quebec. It emerged in 1899 following a reorganization by its predecessor, the Central Vermont Railroad. The CVRY came under Canadian control in the 1920s and was finally sold off in 1995.