Green’s Dictionary of Slang

(US) a fast freight train.

1915		Morn. Tulsa Dly World (OK) 13 June 19/2: Manifest — A through freight.
1924		‘Digit’ Confessions of a Twentieth Century Hobo 100: Last night I went to the freight yards, saw the conductor of a manifest all made up ready to pull out.
1935		E. Anderson Hungry Men 153: I don’t want to miss this manifest.
1936		Mencken Amer. Lang. (4th edn) 582: In the days before hitch-hiking, hoboes spent a great deal of their time stealing rides on the railroads, and their railroad vocabulary remains rich and racy. [...] a fast freight is a manifest or red-ball.