Police in Germany said Thursday they were investigating the appearance of swastikas painted with human blood and smeared on dozens of cars, some mailboxes and building facades in the central town of Hanau.

Police spokesman Thomas Leipold said officers were alerted Wednesday night when a man reported that he noticed the shape of a swastika applied in a reddish liquid on the hood of a parked car.

A special test quickly revealed that the substance was human blood.

Police said that in almost 50 cars in total had been defaced in a similar way.

“The background is completely unclear,” Leipold said, adding that investigators did not know if specific cars, mailboxes and buildings were targeted or if the swastikas were applied randomly. He said that there were also several other scribblings on cars and buildings which he could not further identify.

There was no indication who is behind it or where the blood came from, Leipold said. He added that officials were not aware of any injuries in connection with the incidents.

For now, police are investigating property damage and the use of symbols of unconstitutional organizations.

The display of Nazi emblems, including the swastika, is illegal in Germany. The swastika is widely considered a symbol of hate that evokes the trauma of the Holocaust and the horrors of Nazi Germany. White supremacists, neo-Nazi groups and vandals have continued to use it after the end of World War II, to stoke fear and hate.

Hanau was in the headlines five years ago when a German attacker shot and killed nine people with immigrant roots in a rampage at a hookah bar in the town, in one of the worst cases of domestic terrorism since World War II.