Call sign
From Tardis Wiki, the free Doctor Who reference
Space Station W3 used the call sign LX88J. (TV: The Wheel in Space [+]Loading...["The Wheel in Space (TV story)"])
The Intrusion Counter-Measures Group used call signs such as Red Four, used by Rachel Jensen; Red Six, used by a van driven by Mike Smith; Red Nine, Blue One, Blue Four and Blue Six. (TV: Remembrance of the Daleks [+]Loading...["Remembrance of the Daleks (TV story)"])
The Brigadier and other members of UNIT often used variations of Greyhound and Trap as call signs. (TV: The Mind of Evil [+]Loading...["The Mind of Evil (TV story)"], The Claws of Axos [+]Loading...["The Claws of Axos (TV story)"], etc.)