£5

From Tardis Wiki, the free Doctor Who reference
£5
A £5 note from a parallel Earth. (COMIC: Who's Who?)

In or prior to 1997, Britain introduced a £5 coin. (TV: Battlefield)

In the 1970s, The Third Doctor and Sarah Jane Smith discovered that they had been sent to a parallel universe because £5 notes had a picture of Edward IX. (COMIC: Who's Who?)