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Probably either the BR Blast or DMR Concrete skins.
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Most likely. Though its not out of the question to think the codes could be for a new game. McFarlane made Assassins Creed figures in August 2013 with unlockable content even though ACIV wasn't out for a couple months.
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Well there's no way to get the Blast and Concrete skins in Halo 4 yet, so it'd make sense.