Perhaps it indicates battery level, other than that no ideas

I'm gonna say this is fake.  Nintendo's only real hint about what it would look like was that the two screens would be less separated so as to better make them create one single large image.  This image has the same distance between screens, also I don't see why one widescreen and one full screen would be a good idea, you'd have a T shaped viewing space and that's just weird. You also have to question where the speakers are gonna be located because if the screen takes up all that space alone I doubt they can fit it right under there very easily and still have quality sound.

Highly doubt it. Nintendo has already stated the two screens will look like one. However, if this turns out to be true, then we could say we have a psychic here.