The coat of arms said "integrity." Now it says "Trump."

The British are known to take matters of heraldry seriously, and Mr. Trump’s American coat of arms belongs to another family. It was granted by British authorities in 1939 to Joseph Edward Davies, the third husband of Marjorie Merriweather Post, the socialite who built the Mar-a-Lago resort that is now Mr. Trump’s cherished getaway.

In the United States, the Trump Organization took Mr. Davies’s coat of arms for its own, making one small adjustment — replacing the word “Integritas,” Latin for integrity, with “Trump.”

Joseph D. Tydings, a Democrat and former United States senator from Maryland who is the grandson of Mr. Davies, learned that Mr. Trump was using the emblem, at least at Mar-a-Lago, when he visited the property. Mr. Trump had never asked permission.

“There are members of the family who wanted to sue him,” said Mr. Tydings, a lawyer who wears his family’s coat of arms on a ring. “This is the first I’ve ever heard about it being used anywhere else.”