The Vatican post office Friday issued a set of stamps for use during the "Sede Vacante", or Vacant See, created by the historic resignation of pope Benedict XVI.

The unusual interregnum stamps, a series of four, include the Vacant See symbol -- a striped umbrella over crossed keys -- as well as the words Sede Vacante, Citta del Vaticano and MMXIII, the year in Roman numerals.

The collector's items are valid until a new pope is elected in a conclave next month. They are expected to become especially valuable if postmarked on the first day.

The special postmark for the stamps reads simply Sede Vacante MMXIII.

The stamps have a face value of 70 euro cents (about $0.91) for Italy, 85 cents for Europe and the Mediterranean, two euros for Africa, Asia and the United States and 2.50 euros for Australia.

The tradition of commemorative stamps to the "Sede Vacante" dates back to 1939.

[Image via Agence France-Presse]