Green’s Dictionary of Slang

the text of a graffitto proclaiming the excellence of a star, a local gang etc, e.g. Eric rules; often ext. as — rules OK.

1973		(con. mid-1960s) J. Patrick Glasgow Gang Observed 30: In the toilet I read a large spray-painted slogan: Wild Young Catholic team Rules O.K.
1976		P. Theroux Family Arsenal 9: The ditch wall was streaked with exulting paint: arsenal rule.
1983		P. Reading 5x5x5x5x5 3v: Bad Skins Rule OK.
1994		Eble Campus Sl. Apr. 7: rule – do well, be great: ‘Pearl Jam rules!’.