Green’s Dictionary of Slang

1. a watchman [= charlie n.¹ (1)].

1859, 1860		Hotten Dict. of Modern Sl. etc.
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.

2. the name Charlie/Charley.

1898		Binstead & Wells Pink ’Un and Pelican 149: Bob and his particular chum Oats (which is short rhyming slang for Charley. ‘Oats-and-barley’ it is in full, but the true art of it lies in the abbreviation) [F&H].
1932		‘P.P.’ Rhy. Sl. 5: All right this morning ‘Oats?’.
1969		S.T. Kendall Up the Frog 11: Old oats and barley ’as a lovely Conan Doyle on the back of ’is bushel and peck.