An Angel Imprisoning Sigil is a sigil that if placed in a room it makes it so any angel which entered the room cannot use their powers and imprisons them.
The sigil is used by Castiel and his faction to hold prisoners. It imprisons the enemy angel in the room, but it doesn't prevent them from actually moving unless they are tied down. This is also effective on Reapers. It was used when Ezra, Flagstaff and Tessa were interrogated.