Clockwork Princess question

according to the this quote from clockwork prince“Patriotic?” Will looked smug. “I’ll tell you what’s patriotic,” he said. “In honor of my birthplace, I’ve the dragon of Wales tattooed on my—” Will has a tatoo somewhere that shouldnt be mention in public i didnt believe it at first but then in clockwork princess Tessa said "After all you weren't lying about that tattoo of the dragon of Wales, were you?” i believe. which brings the question where is the tatoo. i have a friend who thinks its on his butt but i think its somewhere else which in her opinion makes me more of a pervert than she is, anyway can someone settle this by proving where it is?