The District of Columbia’s top federal prosecutor says he will investigate a protester who on Monday held a sign that implied President Trump and Elon Musk should be assassinated. The poster invoked Luigi Mangione, who has been accused of murdering a health insurance company’s chief executive. 

On Monday, more than a dozen protests across the country were held to demonstrate against the president and the head of the Department of Government Efficiency. The protests were organized by a new group called the 50501 movement, which aims to raise awareness about Messrs. Trump and Musk’s actions to shut down parts of the government and cut funding to executive branch agencies. 

At the Washington protest near the Capitol Building on Monday, a man was seen holding a sign that invoked Mr. Mangione. The sign read: “Elon, Don, Luigi Says: Deny, Defend, Depose,” which refers to a message Mr. Mangione wrote on a bullet casing that was found near the body of the United Healthcare chief executive, Brian Thompson. The sign included a drawing of the character Luigi from the Mario Brothers video game franchise. 

The acting U.S. attorney for the nation’s capital, Ed Martin, wrote on X that he and his team were going to investigate the incident. 

“Threats against public officials at all levels — whether it be the president or a line federal worker — must stop. Our safe and beautiful capital city cannot be the home of such dangerous conduct from any side, at any time,” Mr. Martin wrote. “We are on the case.”

The video was first posted to X by notorious conservative activist Laura Loomer.

After that was first posted, Mr. Musk himself boosted the post by tagging Mr. Martin and asking him to take a look at the protester. 

“Advocating murder of the President is a serious crime and they have the gall to do so on President’s Day! Letting @EagleEdMartin know about this,” Mr. Musk posted, tagging the U.S. attorney’s personal X account. 

Protests against Messrs. Trump and Musk which were sanctioned by the 50501 movement cropped up coast-to-coast, with more than 1,000 rallying at the nation’s capital. Other protests were held at major cities like Austin, Tallahassee, New York City, and Cincinnati, among others. 

Organizers for the 50501 movement did not immediately respond to an email seeking comment. 

Public acrimony against Mr. Musk has grown steadily in recent weeks, as he and his team have accessed vast swaths of the federal government, and successfully shut down the U.S. Agency for International Development. At Portland, Oregon just last week, a man was caught on camera spraypainting the word “Nazi” onto another man’s Tesla, according to a local outlet, KGW8. 

Another tech-focused outlet called Futurism reported last week that Tesla owners in California have also been threatened by individuals who seemingly disapprove of Mr. Musk’s role in the government. According to the outlet, Tesla owners in four California cities said that someone left threatening messages tied around bricks on their cars, demanding that they sell their vehicles by February 12 or they will be vandalized. 

Tesla dealership in the Netherlands and Colorado, and a Tesla factory in Germany were similarly vandalized in recent weeks with messages implying Mr. Musk is a Nazi.