Death Omen

Usually, a death omen is an indicator that the person who is visited by it is going to die. Sometimes the apparition can manifest in several places at once (bilocation).^BoM

Death Omens in "Supernatural"

In 2.07 The Usual Suspects, the ghost of Claire Becker is a death omen who is the ghost of a woman killed by crooked Detective Pete Sheridan. She appears to people he is about to murder. She tries to communicate and generates the letters DANASHULPS through printers, and computers. This is an anagram of Ashland Sup(plies), where she was killed.

When Detective Ballard kills Sheridan, Claire is at rest.

In 3.06 Red Sky At Morning the ghost ship Espírito Santo appears to people who have murdered a member of their family, before they are killed by the Vengeful Spirit of the Captain's brother. The ship also appears to Bela, who does not elaborate on the reason.

After the brothers summon the spirit of the Captain and the two spirits merge, the ship is not seen again.