I'm not sure if it's exactly his tattoo (it looks slightly different from what I recall, though I didn't usually see it at that angle...) but the pixiv description seems to suggest it definitely is either supposed to be his, or based on his since the artist seems to mention watching FMA. The tags might be of use in making more sense of it, but I can't properly translate 'em.
(On a side note,the radioactive symbol on the palm makes me think of Kimblee.)