My mouth piece simply certified
Something certified has been recognized as meeting some predetermined standard for quality. For diamonds specifically, there is a pretty thorough and well-defined certification process. Paul’s grill and the diamonds therein have apparently been certified by a licensed grillologist.
To help improve the meaning of these lyrics, visit "Grillz" by Nelly (Ft. Ali, Brandi, Gipp, Jermaine Dupri & Paul Wall) Lyrics and leave a comment on the lyrics box