Green’s Dictionary of Slang

1. an act of informing committed by innuendo, or even error, rather than by direct accusation.

1985		Southern Illinoisan (Carbondale, IL) 7 Apr. 4/1: Prison Slang [...] Dry snitch: Snitching without giving specifics — for example, an inmate who calls out to alert a guard about an impending attack or escape in progress, without saying exactly what is happening.
1990		S. Morgan Homeboy 44: It was a dry snitch that came down at San Quentin.
2002		J. Lerner You Got Nothing Coming 235: ‘How about you just sort of sing out a name or two, like it’s part of a rap song or something. That wouldn’t be snitching.’ The Bone [...] shakes his head. ‘Nah, O.G. That would be a dry snitch.’.

2. an individual who passes on information in this manner.

2003

G. Pelecanos Soul Circus 165: ‘They be trying to talk to everyone knew Phil and Granville.’ ‘They tryin’. Except for some dry snitches they got inside, though, they ain’t had too much success.’.