On August 21, 2013, the monument was painted pink to commemorate the 45th anniversary of Prague spring. Prague spring refers to the 1968 invasion of Czechoslovakia by armies from five Warsaw Pact countries – the Soviet Union, Poland, Hungary, Bulgaria and East Germany-- to crush Czechoslovakia's democratic reforms. One hundred and eight people were killed with many more seriously injured.
The painted inscription says, in both Bulgarian and in Czech, "Bulgaria apologises."
The relief has also been used to protest the arrest of Pussy Riot, the recent Russian invasion of the Ukraine, and the Katyn Massacre (Russian's 1940 massacre of 22,000 Polish prisoners and internees, including military officers, doctors, etc.) These paint jobs incense the Russian government.
The Bulgarians have now installed surveillance cameras around the monument.
