Green’s Dictionary of Slang

L.K. Clark n.

also Elkie Clark

[rhy. sl.; ult. Elkie Clark, a Glaswegian boxer in the 1920s–30s]

the mark, i.e. beginning.

1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.
1998		R. Puxley Fresh Rabbit.