On 15th March 1917 (2nd March by the Julian calendar used in Russia), Tsar Nicholas II abdicated and a Provisional Government was formed. Shortly afterwards, the so-called 'Revolutionary overprints' on Romanov and currency issues, appeared in the stamp trade.
There are three different overprints:
TYPE I: Phrygian (Liberty) cap and two crossed swords with inscription 'Fraternity - Equality – Liberty' in Cyrillic, overprinted in red over a block of 4 stamps.
TYPE II: Reproduction of a special issue of the 'Isvestia of Petrograd Sovie' newspaper from 16th March (3rd March), announcing the abdication of the Tsar and his brother, overprinted in black over a block of 8 stamps.
TYPE III: Reproduction of the first page of the 'Isvestia of Petrograd Soviet' newspaper from 17th March (4th March), with a complete text of the abdication overprinted in black, over a block of 12 stamps.
Various errors such as inverted and double overprints exist.
Although there are several covers known to have been sent through the postal system, these overprints did not have any official authorisation, and are regarded purely as private speculations. Nevertheless, like most of the early philatelic fantasies, they are very popular and eagerly sought after by the specialised collector.