The Red Army liberated Vienna from the Nazis. The soldiers went street by street and checked to see if there were any snipers or traps. On the corner of the houses they left an inscription: "Provereno", meaning: checked out. This is the only plaque Austrians have kept since then.
Extremely recommend spending two hours in Vienna with guide Tom. He tells the stories of the city and its history in the short, interesting and elegant way. The trip starts from Stephan Platz, passes through the streets of Graben, the Jewish quarter, Am Hof and ends at Ferstel Palace and the Mekler cellar.