The image of this pin is the Decembrists Memorial Monument in St. Petersburg.
The Decembrist revolt or the Decembrist uprising, took place in Imperial Russia on 26 December 1825. Russian army officers led about 3,000 soldiers in a protest against Tsar Nicholas I. Because these events occurred in December, the rebels were called the Decembrists. As you figured. The experiences of the Napoleonic Wars and realisation of the suffering of peasant soldiers resulted in Decembrist officers and sympathisers being attracted to reform changes in society. They displayed their contempt of court by rejecting the court lifestyle, wearing their cavalry swords at balls (to indicate their unwillingness to dance), and committing themselves to academic study. These new practices captured the spirit of the times as a willingness by the Decembrists to embrace both the peasant and ongoing reform movements from intellectuals abroad.
There was a standoff at the Winterpalace between loyalist soldiers and the rebels. Later that day the rebels lost and most of them arrested. 5 rebels were executed and the rest went into exile to Siberia.