As we've reported, Cherrystone's upcoming auction of world stamp rarities next month includes some extremely exciting Chinese rarities including a 1923 red surcharge invert and 1941 Dr Sun Yat-sen invert.

However, those specialising in US stamps and errors wouldn't forgive us if we didn't mention a particularly attractive example of a truly classic error: the CIA invert. In fact there is a whole block of four available.

Dating back to 1979, the only known source of the stamps was bought by a CIA employee whilst he was in working hours (hence the name, and hence why the US authorities tried to claim that the stamps belonged to them).

The error was caused, as is usually the case with stamp inversion errors, by the need for multiple printings. The otherwise fairly bland design of the candle was supposed to be enhanced by a bright, white & orange colour set slotted in separately, in order to give a vivid visual metaphor to the line 'America's light fuelled by truth and reason'.

CIA stamp invert block (never hinged, and in very fine condition)

Unfortunately the coloured addition was applied with the stamp sheet the wrong way up, leaving it as a rather puzzling, explosive exclamation mark at the base of the candle stand.

Only around 90 examples of the stamp exist, which is similar to the number of Inverted Jennies in existence, but the CIA invert doesn't have quite the same status, and so examples tend to sell for low five figure rather than six-seven figure sums.

Nevertheless they would make a fantastic centrepiece to most collections, and we like them so much we included them in our Top Five stamp inverts list.

Cherrystone's CIA invert block is expected to sell for around $60,000 in their New York sale on December 7-8.