Police in Frederick, Md., are investigating the distribution this week of at least 30 racist fliers that appear to be linked to a Ku Klux Klan group, officials said.

“It’s disturbing and upsetting,” said Michele Bowman, a spokeswoman for the Frederick Police Department. “Hopefully we can identify who did this.”

She said that officers gathered up the fliers Thursday in a diverse neighborhood just outside downtown Frederick. The fliers had been placed inside clear plastic bags that were weighed down with birdseed and left on residents’ driveways. Police sent a group email to residents of the neighborhood, asking if anyone had seen anything suspicious or might have useful surveillance camera footage.

“We’re hoping someone comes forward,” Bowman said.