Angel's Wings

When Angels die after being stabbed by an Angel Blade, shadows of their wings are burned into the surface on which they are lying, as seen in the opening of "On the Head of a Pin]" when Castiel finds a female angel dead on a street, and again when Anna kills Uriel and when Zachariah and Gabriel were killed. Also, in "Dark Side of the Moon", Zachariah tells Dean and Sam that in his true form he has six wings and four faces, one of them being that of a lion. It's possible that the number of wings an angel possess represents their rank or power since Castiel was shown to have two wings, while Zachariah, his superior, has six. However, this doesn't always apply, as Archangels only have two but they're stronger than Seraphs.