The numbers “86 47,” used by some to protest President Donald Trump, appeared etched into the National Mall in Washington, D.C. on Thursday, prompting an investigation by the U.S. Park Police, though the cause of the marks is not yet known.

Markings appearing to read "86 47" were etched into the National Mall on Thursday. (AP Photo/Julia Demaree Nikhinson)

Images captured of the National Mall on Thursday show a clearly defined “eight” and other fainter numbers etched into the grass that appear to make up the phrase “86 47.”

The “86 47” phrase has been used by some as a protest slogan against Trump, while Trump has previously called the phrase a call for “assassination,” as “86” is a common slang term to mean “throw out” or “get rid of,” according to Merriam-Webster, and Trump is the 47th President of the United States.

The U.S. Park Police told Forbes in a statement it responded to a report of vandalism on the west lawn of the Washington Monument around 11:30 a.m. EST, noting the numbers “86 47” were marked into the grass.