Tony's tattoo is from Dante's Inferno:
It's a bit difficult to read, because it is based on the calligraphy of a 14th century manuscript. It is the final line of the poem, "E quindi uscimmo a rivider le stelle." Canto XXXIV, line 139. Translations treat this line in different ways, but I prefer the one that William Styron cites as the final line in his memoir, Darkness Visible: "And so we came forth, and once again beheld the stars."