No, I have no idea what "Rock Justice" means, unless it was some allusion to the ironic lack of recording contract offers. In any event, the song has the common enough folk/blues theme of the wrongly condemned man. (In fact, it's an updated "Poor Boy," which was one of the first things I recorded.) The music, too, follows traditional folk/blues patterns, except for the occasional perky (if erratically-played) excursions into . . . I dunno, elevator jazz or something.
Anyway, for a song written on the spot mainly for giggles, it had its moments, though they were still few and far-between.