Green’s Dictionary of Slang

1. (US Und., also sherlocko) a police officer or detective.

1902		‘Hugh McHugh’ Back to the Woods 57: ‘Down there, eh?’ snorted the country Sherlock, getting on his knees and peering into the depths.
1922		Smith’s Wkly (Sydney) 2 Dec. 18/3: ‘Wotcher lookin’ for now?’ ‘I’m lookin’ for your damned hooks,’ roared silly Sherlock.
1943		R.L. Bellem ‘Shakedown Sham’ Dan Turner – Hollywood Detective May 🌐 Now, then, Sherlock! [...] Suppose you tell me what goes on!
1944		C.B. Davis Rebellion of Leo McGuire (1953) 162: That’s the way it works. You think you’re wise because you outdraw the metropolitan sherlockos and a town whittler knocks you off.
1951		Kerouac On the Road (The Orig. Scroll) (2007) 223: This flabbergasted Sherlock and he went back in the station house.
1965		F. Pollini Glover 302: These Sherlocks are quite eager to start looking around.

2. (US campus) a friend.

1996

Eble Sl. and Sociability 102: Homebiscuit, homechop, homeslice, homey, and sherlock are all developments of the notion of kinship between people from the same hometown.