Photo by Tim Brown.

U.S. Park Police say they’re investigating after visitors discovered a noose inside the Smithsonian National Museum of African American History and Culture.

The noose was found by tourists on Wednesday afternoon at the museum’s exhibit on segregation, according to the museum. Park police removed it, and reopened the gallery within three hours, according to Smithsonian officials.

This comes less than a week after a noose was found in a tree near the Hirshhorn Museum last Friday. Nooses have also been found recently at local college campus like University of Maryland and American University.

“The noose has long represented a deplorable act of cowardice and depravity—a symbol of extreme violence for African Americans,” Lonnie Bunch, the museum’s founding director, said in a statement. “Today’s incident is a painful reminder of the challenges that African Americans continue to face … This was a horrible act, but it is a stark reminder of why our work is so important.”