Peace 12 is a slang term for goodbye. Deriving from the words 'peace' and the words 'one' which also mean goodbye. The movie Belly showcases the term 'One', and one day John Hensley and Zach Fowler watched the movie and said, hmm, wow, One is such a ridiculous thing to say when saying bye. So Peace 12 was created in the action of making fun, and now it is a worldwide phrase.
John: hey man, i'm gonna get goin.
Zach: alright, well, peace 12 dawg.