Paper money
From Tardis Wiki, the free Doctor Who reference
Kublai Khan dealt in paper money rather than gold. (TV: Marco Polo)
In England, paper bank-notes were issued by the Bank of England. The Third Doctor carried a bank-note with the image of Queen Elizabeth II. (COMIC: Backtime) In a parallel universe, the image of King Edward IX five pound note in the 1970s. (COMIC: Who's Who?)
