Green’s Dictionary of Slang

1. (Aus.) a shepherd, a musterer, one who mends boundary fences [? the speed of his progress].

1897		Worker (Brisbane) 4 Sept. 8/4: By ‘lizards’ he means musterers, sometimes he calls them ‘snails’.
1945		Baker Aus. Lang. 63: Shepherds have been known variously as lizards, crawlers, snails and motherers.

2. (US) a freight train [its (lack of) speed].

1887		Daily Trib. (Bismarck, N.D.) 23 Oct. 4/1: An express train is a ‘flyer,’ a freight train a ‘snail.’.
1941		D. Burley N.Y. Amsterdam Star-News 20 Sept. 15: They pop in on the snail with many twirlers like rubbernecks.

3. (US tramp) a cinnamon roll or bun [? its shape].

1908		Wathena Times (KS) 28 Aug. 3/1: Try Stephan’s coffee cake and snails.
1918		El Paso Herald (TX) 9 Feb. 10/4: ‘Have you tried our celebrated Danish Coffee Snails>’.
1920		F. Williams Hop-Heads 62: I went into the dairy lunch, ordered a cup of coffee and a ‘snail’.
1934		G. & S. Lorimer Stag Line 166: ‘Nothing in sight but these sinkers and snails. Whole plate of ’em.’ [...] ‘These snails are pretty tasty.’.
1940		‘Argot of the Sea’ in AS XV:4 Dec. 450/2: coffee an, coffee and. Coffee and sinkers (doughnuts) or coffee and snails (cinnamon rolls).
1948		Quad-City Times (Davenport, IA) 20 Sept. 12/1: he saw ‘coffee and snails’ on the menu.
1958		Times (San Mateo, CA) 4 Sept. 11/8: Turnbull [...] served coffee and snails to teachers and parents.
1962		Ragen & Finston World’s Toughest Prison 818: snails – Cinnamon rolls.
1971		Sheboygan Press (WI) 9 Feb. 16/4: Root’s Monday Morning Koffee Klatch [...] Doughtnuts [...] Snails.