"And lest you question that reveal as perhaps a piece of misdirection, executive producer Eoghan Mahony,
who wrote the episode “The Red Tattoo,” assures TVLine, “That is a
legit clue, and it is a big deal. Now Jane’s got his leverage.”"
http://tvline.com/2013/10/27/the-mentalist-new-clue-red-john-shoulder-tattoo/