A noose was found hanging from a tree outside of the National Gallery of Art Saturday afternoon, the third of this type of incident in the last few weeks.

The U.S. Park Police is investigating after the rope was found around 3 p.m., Sgt. Anna Rose told the Washington Post.

A noose was discovered on the first floor of the National Museum of African American History and Culture in May, according to WRC. Another noose was found at the Hirshhorn Museum a few days before that.