Green’s Dictionary of Slang

comet n.

(US tramp) the aristocrat of tramps, travelling only on express trains and only for lengthy journeys.

[US]J. London Tramp Diary in Jack London On the Road (1979) 59: The quiet easy going, the slow pokes & the comets.
[US]J. London ‘Rods and Gunnels’ in Bookman XV Aug. 541–44: It is as a ‘comet,’ one who has served his ‘road-kid’ and ‘gay-cat’ apprenticeship, that I shall speak.
[US]‘A-No. 1’ From Coast to Coast with Jack London 123: At Reno every hobo, ranging from the aristocratic ‘comet’ down to the lowliest of low ‘grease balls,’ registered his moniker.
[US]P. & T. Casey Gay-cat 144: The Frisco Kid, a blowed-in-the-glass, a comet and a hobo royal!
[US]Irwin Amer. Tramp and Und. Sl. 53: Comet. – A tramp new to the road, or to tramp life. So called since these persons are invariably nervous, inclined to move quickly when any one seems to be watching them, and worried lest they be arrested. Also a tramp or hobo, usually with a decided psychosis, riding only fast trains, and for long distances, even though there be no reason for such moves.
[US]Monteleone Criminal Sl. (rev. edn).