Russell Baze, the main protagonist of Out of the Furnace, has a quite prominent tattoo on his neck, which on a closer look seem to be the numbers 15104 or something similar:
While there might very well not be much more to this tattoo, it seemed too omnipresent to me during the whole movie to just be ignored as merely ornamental. I thus wonder if there is any further significance to this tattoo that would tell us something more about his character. Neither did the movie seem to give any explanation, but maybe I just don't have the necessary cultural background information, or it has been adressed in external interviews or the like.