The World War II Memorial, the Lincoln Memorial, the D.C. War Memorial and the Washington Monument were vandalized with permanent marker over Presidents Day weekend.
Crews are working to remove the graffiti which was reported by a visitor at 1 a.m. on Sunday. It appeared at the Lincoln Memorial about 11 p.m. Saturday.
"Somebody appears to have, with Sharpie or magic marker, tagged similar messages at the Lincoln Memorial, on the Washington Monument and at the World War II Memorial," said Mike Litterst of the National Park Service.
Similar graffiti appeared on street signs and utility boxes along the National Mall, according to NPS.
One U.S. serviceman who took his family to the Lincoln Memorial Tuesday takes the vandalism personally.
"I served the greatest air force in the world, but to come here to see that is like a slap in our face," Kevin Hall said.
The graffiti was described as not overly political nor hate-filled. It covers a fairly small area at each of the vandalized memorials with several lines of text.
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The words are difficult to read or make sense of, but the clearest graffiti on a steel electrical box appears to say: "Jackie shot JFK;" "blood test is a lie, leukemia, cancer HIV get a second option;" and "9/11/01 ... pilots fly planes into WTC."
Authorities believe the same person is behind all the graffiti but haven't ruled out others were involved, Litterst said.
"The similarity of what's written and you know, the handwriting style," he said.
Defacing a national monument or memorial is rare but not unheard of. The most significant case in recent memory was a bizarre incident in 2013, when a woman threw green paint on the Lincoln Memorial and later at the Washington National Cathedral. She was arrested but later found incompetent to stand trial.
Lincoln Memorial Vandalized
In that case, it took crews nearly a month to clear the green paint from the Lincoln Memorial, but NPS staff are skilled in the tricky removal process of graffiti removal, Litterst said.
The staff are using a pressure washer and solvent, safe for historic stone, to remove the graffiti. The Lincoln Memorial, Washington Monument and World War II Memorial were cleaned Tuesday. Cleaning at other locations will continue this week.
"Something like marble, which is more porous than granite, may have a different way to take it off," he said. "Sometimes it takes multiple cleaning and cleansings to get it to come out, but of course, in the course of getting it off... we don't want to do any further damage to the stone."
U.S. Park Police are reviewing surveillance camera footage from the locations.
The memorials had more visitors than usual over the weekend due to unseasonably warm temperatures.