The Pinkerton National Detective Agency, founded by Allan Pinkerton in the 1850s, is most commonly associated with railway duties, particularly during the Civil War and afterward. Pinkerton agents were often employed to protect railroad infrastructure and personnel, investigate crimes, and ensure the safety of trains and cargo.
While they did have involvement in other areas, such as providing bodyguard services (notably for President Abraham Lincoln), their most significant association stems from their work with railroads. Therefore, based on the historical context, you would most expect a company from the name "Pinkerton" to perform railway duties.