The underside of his arm bears three words: Silence, Exile, and Cunning, taken from the book A portrait of the Artist as a Young Man by James Joyce.
The bird just visible in this picture is from the card game Rook. He has a number three on his left hand.
He has said: "Three is a sort of special number for me. It's a very creative number. Triangle, trinity - you know, two people make another person. Three is a mystical, magical number."