Authorities are investigating a possible hate crime after a sign honoring a civil rights hero was defaced in St. Louis.

The Missouri Department of Transportation removed the sign marking "Rosa Parks Highway" because it had been spray-painted with the letters "KKK," which is an abbreviation for the Ku Klux Klan white supremacist group.

St. Louis County Police dispatched their crime scene unit to investigate early Friday morning.

According to KSDK, the Ku Klux Klan had at one time sponsored the Adopt-A-Highway litter control program on that stretch of Interstate 55. But their sign was taken down after lawmakers dedicated the road to Parks.

Watch this video from video from KDSK and KMOV, broadcast Jan. 20, 2012.

(H/T: Think Progress)