Hey, waaaaaait a minute...

[gmonkey42]

I was just thinking about how Gary Oldman has those markings in PoA and people have speculated that they're part of being an animagus. That sounds reasonable to me, except for a few things: it seems like that would make being an undregistered animagus more risky, since anyone who saw one with their shirt off would know. And then it occurred to me that McGonagall would have blue tatoos all over her wrinkly body. Eeeeew.