My initial theory, apropos of very little was that Ink knew something was coming, and was worried that if he turned he would forget all of the knowledge he thought he would need- hence the last minute tattoos, which were a way of ensuring that he wouldnt lose his notes, no matter what.
Sort of like writing on your arm to cheat in an exam I guess. The problem with that theory, of course, is that head and hands seem to be a rather odd choice of where to put the tattoos. And he seems to have finished off the job with the tattoo gun in the mental ward of
the hospital.