The Doctor's psychic paper

The Doctor, throughout their lives, carried a card of psychic paper.

History
The Second Doctor was given psychic paper while employed as an agent by the Time Lords' covert organisation, the Celestial Intervention Agency, which had developed the technology. He and the Time Lady Serena used it to attend the Duchess of Richmond's ball to keep an eye on the Duke of Wellington. (PROSE: World Game)

Just prior to Earth Death in the year 5,000,000,000, the Ninth Doctor used his psychic paper to pass himself off as a guest, under the name "the Doctor", with Rose Tyler as his "plus one to the steward of Platform One. (TV: The End of the World)

Aboard Satellite Five in the year 200,000, the Ninth Doctor used psychic paper to pass himself off as being from management to Suki Macrae Cantrell and Cathica Santini Khadeni. (TV: The Long Game)

Searching for a Chula ambulance which crashed to London in 1941, the Ninth Doctor used his psychic paper to pose as a Doctor John Smith from the Ministry of Asteroids. (TV: The Empty Child)

In 5,000,000,023, the Tenth Doctor received a message on the psychic paper instructing him to come to Ward 26 of the New New York Hospital. As he discovered, the message was sent by the Face of Boe. (TV: New Earth)