What is "f-man"

F-Man is a 1936 American comedy film directed by Edward F. Cline and written by Richard Connell, Henry Johnson, Paul Girard Smith and Eddie Welch. The film stars Jack Haley, William Frawley, Grace Bradley, Adrienne Marden, Onslow Stevens and Franklin Parker. The film was released on May 2, 1936, by Paramount Pictures.