Members of the Public Theater’s Mobile Shakespeare Unit, which is staging a production of Richard III on Rikers Island, are performing under some difficult circumstances: Only after crossing the river from Queens, passing several ID and metal detector checks, and receiving an ultraviolet hand stamp do the actors finally get to see the stage and props they’ll be using (a 14-by-14-foot taped-off section of a gym floor and paper and rattan swords, respectively.) As for “the fans oscillating at top speed,” “telephone ringing in the corner,” and “guard walking by with jangling handcuffs and jingling keys,” there’s nothing the actors can really do except emote, emote, emote.