Green’s Dictionary of Slang

a train guard; a military guard.

1894		Pall Mall Gaz. 4 July 3/2: Overheard at Waterloo Station [...] ‘Is this right for Woking, Bill?’ ‘Dunno, Jim; ask the Christmas’.
1903		Truth (Brisbane) 15 Mar. 1/8: If you hear a bloke on the race platform ask his cobber, ‘When does the rain flow?’ and his cobber says, ‘Go slow; chat de Christmas card,’ [...] one has inquired, ‘When does the train go?’ and the other has replied, ‘Do’'t know; ask the railway guard’.
1910		Eve. Teleg. (Dundee) 3 Aug. 4/1: Owing to the 'Christmas' [...] the 'Andie' waited several minutes at the junction [...] 'Christmas card' (guard), 'Andie Caine' (train).
1923		Eve. Teleg. (Dundee) 11 July 11/4: Christmas (Christmas card) means a railway guard.
1960		J. Franklyn Dict. of Rhy. Sl.
1969		S.T. Kendall Up the Frog 27: Christmas cards – Guards (the) (military).
1992		R. Puxley Cockney Rabbit.
2002		Pete’s Aussie Sl. Home Page 🌐 Christmas card: train guard.