What is this on the bezel of this 15-inch Retina MacBook Pro (early 2013)? I've tried scrubbing it with water and a cotton t-shirt. I also carefully tried to use a sponge and my nail, but it doesn't seem to come off at all. I am beginning to believe it's something under the screen. Is this a known issue or? I'm not the original owner of this MacBook so I don't know what has caused it, but I will text the previous owner who I retrieved it from yesterday and ask.