This is a way to alert the presence of the police, and also to try to bypass successive anti-drug operations in Bairro da Pastelleira Nova in Porto. Next to the public road, in places where drugs are directly sold, drug traffickers strategically piled stones and parallels. Apparently, they will serve to be thrown against the PSP in retaliation. One of the incidents happened on Friday. The 41-year-old PSP agent was stopped at a traffic light on Rua João Mascarenhas after leaving work when a street vendor approached him and asked if he wanted to buy drugs. As soon as he realized that a policeman was driving, he immediately alerted the other drug dealers, who threw stones at the car, which had a broken rear window and partially destroyed the sides. The agent was not injured, and one of the stone throwers was arrested.