Mark Schonherr is part of a story in the story. He’s a character we don’t really meet in person and who doesn’t matter that much in Mirror’s Edge, but his story is told anyway and you will see that the poor guy doesn’t end up quite well.
Mark’s story takes place in chapter "Pirandello/Kruger" because he works there. The first reference to him is an audio message. You will hear it at the beginning of checkpoint B, at the top of a yellow stairwell:
Could Mark Schonherr please report to the chief supervisor’s office, mister Mark Schonherr. Thank you.
After that, you fall down the stairwell and get into an orange room full of SWATs shooting at you. If you get rid of them and look around the area, you will find several offices with desks, including Mark’s. On his desk you will find the following note:
Later, you get into a small room to push a button (not far, there is a forklift). In this room, there is a computer displaying the following email that Mark sent to someone called Christian Plowforce:
Read the last sentence of this mail carefully because it’s tied to the next "reference" made to Mark.
Later in the level, you get in a white corridor with dark windows on both sides. If you get close to the second window on the left, you will see this:
This man probably is Mark Schonherr who couldn’t escape the extreme security of Pirandello/Kruger.
This little story is not very important in Mirror’s Edge, but it adds some nice details to the whole thing and shows us that Pirandello/Kruger is not to be trusted and can hold and torture anyone who disagrees with its actions.