Doppelgänger, a ghostly double of a living person, often seen as a harbinger of bad luck or oncoming death.

Black Shuck, a ghostly black dog often seen as an omen of death or bringer of bad luck. If you think the Black Shuck is passing by, it’s recommended you shield your eyes and look away: if you never see the creature you might avoid the curse.

Crows, which are often seen as a negative omen, signaling death or doom. Obversely a dead crow is said to be a positive omen, but I have hard time believing a dead animal could ever be a sign of something good.

Banshee, a female spirit who announces the death of a family member with her cry. Sometimes she is described as a hound woman with a beautiful voice, other times an elderly woman with a haunting wail or shriek.

“The Great Hop”

For the Black Rabbit prompt, though not really related to any sort of omen in particular.

For the prompt "White Horse", but not related to any specific omen.

Owls are said to be good or bad omens depending on the surrounding circumstances. Something tells me this may not be a good sign.

For the “Umbrella” prompt, but once again not related to the omen.