Several years before 2008 or 2009, Bobby visited a house in Tennessee where a Soul Eater was in residence. Unable to defeat the monster and with nothing else to fall back on, Bobby tried the sigil and succeeded in trapping the monster. He remained unaware of what he'd used the sigil on for years.
In 2008 or 2009, Bobby got called on a case by Rufus Turner who was facing another Soul Eater. Bobby recognized the monster from his previous encounter with the species and introduced the sigil as a way of trapping it. While attempting to draw the sigil, Bobby was pulled into the Soul Eater's nest where the Soul Eater possessed Bobby to attack Rufus. Rufus was able to subdue Bobby and finish the sigil, trapping the Soul Eater and forcing the souls of its living victims from its nest. However, the souls of those who were not still alive remained behind. To prevent the sigil from being broken, Bobby put up new wallpaper over the sigil.
In 2016, a woman remodeling the house inadvertently broke the sigil, releasing the Soul Eater. After determining what they were dealing with, Sam Winchester found a new sigil that could kill a Soul Eater so the trap was not repeated.
The sigil has to be painted on a wall of the house in red paint. Once completed, it traps any monster affected by it such as a Soul Eater and if the monster is possessing someone, expels them from the person's body. The souls of anyone living trapped by a Soul Eater will be forced from its "nest" by the sigil, but anyone who doesn't have a body to return to remains trapped.
Breaking the sigil breaks the trap and instantly frees the monster.