Angel Banishing Sigil
The Angel Banishing Sigil must be drawn in the blood from an angel's vessel. It temporarily banishes angels (except the one who drew it) from that location.
4.10 Heaven And Hell
When Sam and Dean join Ruby who has hidden Anna Milton from Alistair, Castiel and Uriel appear and proclaim they must kill Anna. As the angels attack, Anna, cuts herself and draws the sigil, sending the angels away.
4.20 The Rapture
When Castiel tries to warn Dean about Zachariah's plan to let the apocalypse proceed, he is captured and forcibly returned to heaven. Sam and Dean find the sigil in the place they were to meet Cass, presumably used by him to try and fight off his captors.
4.22 Lucifer Rising
Castiel uses the sigil to banish Zachariah, when he decides to help Dean get to Sam and try and stop him killing Lilith.
