The National Park Service says graffiti has been found at three monuments in Washington.

WRC-TV reports that words written in permanent marker were discovered over the holiday weekend on stone at the Lincoln Memorial, the Washington Monument and the World War II Memorial. The station doesn't say what was written, but it reports that the graffiti covers a small space and is described as not overtly political or hate-filled.

Park service spokesman Mike Litterst says because of similarities in what's written and the handwriting, it's thought the graffiti was left by the same person. He says park service staffers are skilled in removing graffiti, but they have to be careful not to further damage the stone.

U.S. Park Police are investigating and reviewing surveillance footage from the monuments