Stamp
From Tardis Wiki, the free Doctor Who reference
Stamps were used on letters and postcards.
Jo Grant once used a Doctor Who stamp to send her space-time postcard to Mike Yates. (PROSE: The Dark Scrolls of the Valeyard)
On the postcards sent by the Doctor to their companions, there were stamps of: a space station, Elizabeth X, Tiaanamat and a Kerb!am Man. (PROSE: From the universe with love!)
The Thirteenth Doctor noted how Hakim Khan collected junk like stamps. (TV: Arachnids in the UK)
