On 1st March, 1777, Nell Hilton was hanged on the gallows at St. John, New Brunswick. She had been convicted by the British as a spy. However, many will not be bothered about that detail, but for the prophesy that she made before her death. She vowed that she would return to "prophesy rock" near Hilton's Neck on the anniversary of her death whenever war threatened America.
Her apparition was allegedly seen and heard prior to the American Civil War, the Spanish War and World War One. However, there do not seem to be any reports preceding other conflicts since.
For a fascinating account of her life, we recommend you read Haunted America and the link posted below.