User blog comment:Argorrath/Treyarch posts a message of zombies; possibly hinting to a DLC 4/@comment-66.87.118.180-20130801082843

The paper may help.

The first seems to be ripped from a notebook.

The second seems to be framed but I could be wrong.

The third looks like it's on a desk or object that's wooden.

The fourth is just a plain one that I can't tell where it may be.