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Yeah, it was a dharma hatch symbol. I can't remember which it was, though. Staff? Arrow?
But google image search gave me this image, so I must be close.

Yeah, that's what is called an "Easter Egg" it wasn't meant to be seen, it was just a little thing that meant nothing, at least that's what they told me on the bonus disc of the second season.

Yeah, they just put it on for no real reason, but when they shot it the sticker was brighter than it was supposed to be. Now, since that happened the writers might decide to incorporate it in instead. I was watching the bonus disc on the Lost second season DVD and that's what they said, not the them incorporating it in. But they might, they were saying how they're always changing the story line.