MacBook - Strange Mark

This morning I discovered a strange mark underneath my screen after my notebook spent the entire night inside it's case. I didn't notice it last night but this morning it caught my eye. It's a small black mark that I can't seem to rub off with pre-moistened wipes or my finger. I'm very careful with my MacBook so these little things do bother me. I took a few pictures to show you what I mean:

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http://img.photobucket.com/albums/v6...a/S5030764.jpg[/
http://img.photobucket.com/albums/v6...a/S5030763.jpg[/

In some of the photos it shows up a silver mark but that's the reflection of the flash. Does anyone have any idea what it is and how it got there? When I run my finger over it, it feels as if nothing is there.