Museums in New York that exhibit artworks looted by Nazis during the Holocaust are now required by law to let the public know about those dark chapters in their provenance through placards displayed with the stolen objects.

At least 600,000 pieces of art were looted from Jewish people before and during World War II, according to experts. Some of that plunder wound up in the world’s great museums.

New York Gov. Kathy Hochul signed a law in August requiring museums to put up signs identifying pieces looted by the Nazis from 1933 through 1945.

The new rule comes as many museums in the U.S. and Europe are also reckoning with collections that contain numerous objects looted from Asia, Africa and other places during centuries of colonialism.

It isn’t clear how many pieces of art now on display will wind up being labeled as Nazi loot, and disagreements have already arisen over certain artworks with a complicated history.

The Metropolitan Museum of Art, in New York City, said it had identified 53 works in its collection as having been seized or sold under duress during the Nazi era.