FF is wrong
going into his mode gives an answer:
A specimen banknote is printed to as a way of checking to see whether or not the design is suitable for putting into full production as a currency issue.
Sometimes, specimen banknotes are printed for distribution to central banks to aid in the recognition of banknotes from a country other than their own.
To avoid its use as a legal tender note the banknote is perforated or punched, given a serial number of 0.9999999999 (all nines) or 0000000000 (all zeroes) or is overprinted with the word Specimen or Cancelled in any language.