Jack Harkness's psychic paper

Captain Jack Harkness, during his days as a rogue Time Agent, carried a card of psychic paper.

History
In 1941, Jack used psychic paper in an attempt to pass himself off to Rose Tyler as an American volunteer of the Royal Air Force's 133 Squadron. However, Rose was able to tell that Jack's credentials were false due to her association with the Ninth Doctor, who also carried psychic paper, as well as the fact that the paper stated that Jack was single and worked out. (TV: The Empty Child)