Green’s Dictionary of Slang

(US prison) to inform by innuendo, or even error, rather than by direct accusation; thus dry snitching n.

1981		Maledicta V:1+2 (Summer + Winter) 264: Sometimes, an inmate goes the route of dry snitching, in which he accuses another of infractions by innuendo, whether intentional or not.
1990		S. Morgan Homeboy 44: Dry snitching in prison carries the same mortal penalty as the real thing.
2015		in Palm Beach Post (W. Palm Beach, FL) 13 Sept. A018/1: You ain’t got talk crazy on Facebook just go handle up cause only thing you doing is dry snitching on yourself.