An Angel Depowering Sigil is a sigil that can depower an angel.
In LOTUS, s part of their plan to cast Lucifer back into his Cage, the Winchesters, Castiel, Crowley and Rowena drew this sigil on the back of a door in a motel room. Once Lucifer was lured in, Sam activated the sigil, significantly weakening his powers. As a result, when Lucifer tried to throw everyone with his telekinesis, they were forced to bend backwards slightly but were otherwise not effected.
The sigil is drawn on a surface and is activated by the caster slapping it with their hand. It is not stated if the material needed for the drawing is blood or simply red painting.