This is a variation of their (the Black Community) favorite chant: "No Justice, No Peace."
That, my friends, is a THREAT. It basically says "this trial must have the outcome we have determined or we will riot." The used it during King, Duke LAX, Jena, and virtually every race-related case involving Blacks.
Fortunately they haven't followed through since King (mostly as a result of police forces having learned from the L.A. riots) but the threat is there, nonetheless.