I had a Russian friend in my school in Tokyo. He was a typical care free guy, who didn’t worry much about anything. So, I met him around 11th of May. Knowing that Russians love 9th of May holiday, Victory Day, I casually asked him how he celebrated it. The guy looked at me, smiled and said: “I’ve got kicked out of my apartment.”
My friend and couple of his Russian friends decided to celebrate the Victory day. So couple of vodkas and some snacks were bought for the occasion. The guys got wasted. While drunk, they decided that they have to honour their grandparents by raising Red flag on top of their apartment, somewhat similar to the picture above.
The police were called, when people on the street saw couple of foreigners standing on the roof of their apartment and waving manically the red flag. To make the story short, the police got involved. No charges were filed, but they were ordered to leave the place ASAP.
So, to answer your question, police would probably ignore you, but you might be punished in other ways. My favorite story from Japan….