IMO Missy Elliott is the worst at this signature thing. Usually she'll whisper something like, "this is a Missy Elliott production/exclusive" but a lot of the time she just graffiti's a whole song with her obnoxious shouting (i.e. Keyshia Cole's "Let It Go" or Tweet's "Turn Da Lights Off"...just to name two examples)

Some of them don't have to say anything. For example, the firetruck sound at the beginning of every Swizz Beatz tracks.