“I’m not surprised,” Mr. Parker said in an interview. “People fear change and when they see change coming, they will try to destroy things. You have a few people out there like that.”

Mr. Parker said the sign should be replaced. So did Annie Wright. Her husband, Simeon Wright, was 12 and sharing a bed with Emmett, his cousin, when he was kidnapped.

“I would keep putting it up, and someone is going to get tired after a while,” Ms. Wright, whose husband died last year, said by telephone. “It’s hatred. It’s all I can say.”

Mr. Weems said that two companies in New York had agreed to design and create a new sign made out of steel, which would be much stronger than the current one, made of a thinner metal. The companies will supply it for free, he said.

For all that Emmett’s case came to signify in the United States, it was largely ignored in the part of Mississippi where he died. There was a highway marker with his name on it, but that too was vandalized when the letters KKK were spray-painted across it. It was later completely covered in black paint.

Mr. Weems said that in the decades after Emmett’s death, people in the Mississippi Delta region wanted to forget about the crime and act as if it never had happened. While that sentiment holds true with some people there, he said, most people in the area have voiced support for preserving Emmett’s story in the historical markers.