Looks like a calender. With a mountain on it.
Doesn't look Easter Egg like to me.
With a Date of October, 2013. Seems suspicious, you have to admit.
it's indeed interesting, thanks for posting it! can you tell me where it was found, is it in one of the recent released demo's or something? it also just might be the month the ps4 is releasing, because I think an Uncharted 4 game at launch is a little to soon, as much as I of course want it, they only have less than 50% of Naughty Dog working on it for only 2 years, for a new platform 2 years is just not enough I think...