Envelope
From Tardis Wiki, the free Doctor Who reference
The Eleventh Doctor had the Teselecta deliver four TARDIS blue envelopes to invite a select few to his "death" at Lake Silencio on 22 April 2011. These envelopes were numbered: 4 was received by Canton Everett Delaware III, 3 was received by Amy Pond and Rory Williams, 2 was received by River Song, while 1 was received by an earlier version of the Eleventh Doctor. The Doctor did not deliver the envelopes personally so as to avoid crossing his own time stream. The younger Doctor observed that the envelopes were perfectly ordinary stationery purchased on Earth. (TV: The Impossible Astronaut/Day of the Moon, The Wedding of River Song)
