Green’s Dictionary of Slang

(US black/campus/teen) goodbye.

1990		Eble Campus Sl. Oct. 3: peace up – goodby.
1996		Eble Sl. and Sociability 101: Peace up and peace out were likewise made popular by rap.
2000		Hip-Hop Connection Jan./Feb. 96: Whoever shot him must be a total wanker. Peace out.
2012		M. Lacher On the Bro’d 18: [I] said peace out to the dickwad at the front desk.