If the signs were mythological creatures:

Aries: Werewolf

Taurus: Hell Hound

Gemini: Doppelgänger

Cancer: Banshee

Leo: Fairy

Virgo: Angel

Libra: Nymph

Scorpio: Ghost

Sagittarius: Mermaid

Capricorn: Vampire

Aquarius: Shapeshifter

Pisces: Siren

(A/N: Am I the only one thinking of Supernatural?)