ID card

ID cards (PROSE: Operation London, Silver-Tongued Liars, A Worthy Successor) also known as identity cards (PROSE: Top Secret) was a form of identification.

UNIT's ID cards were known as UNIT IDs. (AUDIO: The Blue Tooth)

Fake IDs were available. (TV: The Long Game, PROSE: The Party in Room Four)

History
Alien experts from UNIT and other groups wore ID cards which were electrified by Jocrassa Fel-Fotch Passameer-Day Slitheen. Though the electricity was deadly to humans, the Ninth Doctor, being a Gallifreyan, survived and attached his ID card to a Slitheen, resulting in the pain being shared amongst the family. (TV: Revenge of the Slitheen) Just prior to this, Staff Sergeant Annie Frederick remarked on how quickly Number Ten had created the Ninth Doctor's pass. (PROSE: Operation London)

P.R.O.B.E. operatives carried ID cards: Louise Bayliss showed hers to Brittany Mordley in 2008, (PROSE: Silver-Tongued Liars) and Giles and Archie MacTavish showed theirs to the security guard of the Vault, Donovan, in 2011. (PROSE: A Worthy Successor)