A meme that originally started in /v/ and arose around September 2006. /v/ is technically a worksafe board, meaning that users are not allowed to post pornography or anything else objectionable by basic standards that, at least according to the standard of "Worksafe", could conceivably get someone fired from their job. However, since /v/ is pretty much /b/ with video games, this rule is unfortunately almost universally disregarded. Thus, whenever someone posts an NSFW picture, it was typical for a user to shout "I JUST GOT PROMOTED" in an ironic sense, meaning to imply that he actually just got fired for looking at porn at work, and that someone else would be promptly promoted to take his spot in the company. It originally started when Black_Knight flooded every NSFW thread with the post "I just got fired asshole," which only egged trolls on to post more NSFW images, much to the dismay of moderators and janitors. Anonymous later latched onto this idea and created the "Promotions" variation as explained above.
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Promotions guy has received many edits and variations, producing a wide range of versions for a myriad of situations, all with the same meaning: "You're posting NSFW material. Stop it before you get deleted, or promoted". The recurring theme in the edits is the mimicking of the pose, that being the frontward raised arms.
Source: http://lurkmore.com/wiki/index.php?title=Promotions