I'm not sure if it's a square in the corners but I do see where they extend to the sides now.
Hard to tell what it is, I played with rotating one of the diamonds in a 45-degree angle and it doesn't look right. Also debating whether that's a rounded square corner or a circle. The image is too distorted and blurry to be certain so I came up with the squares—when you squint, it could be it.
But even with the high res I don't see any diamond point going to the corner of the inside box.. but that's just me.
Same here, at first I thought they could be angled diamonds but I couldn't get any definition to support that guess, even when adjusting the image to enhance detail. I'm scouring the net for any clues or images that can help make the design more accurate but so far none.
I would cast my vote for a diamond.