The first sigil seen in the series was in the episode Heather. Amelia Blake placed one on the wrist of her friend, Heather Barnes, after a demon had entered her body sixteen years ago during the night of the Boatyard fire. Years later, Cassie wanted to find out what had happened to Heather, since Zachary Larson attacked Cassie and the Circle, blaming them for what Amelia did to Heather. And when Cassie came to visit Heather, she was shocked, seeing Heather's physical state, that her mother would do something like that. In an attempt to reverse her mother's spell, she enlisted the help of Adam and Diana, who refused, and then turned to Faye for help, promising her she could have a look into the Blake Book of Shadows. The two went by night to the house of Heather and her brother Wade and recite an incantation to reverse the effects of the sigil. Thinking it didn't work, they left. But Heather woke up in a strange aggressive state and attacked her brother, before leaving to find Amelia. While discussing with Cassie downstairs, she reveals the symbol her mother used was meant to prevent Demons from possessing people. Meanwhile, Adam and Diana warn Faye about the danger Cassie is facing, but when she goes to find Cassie, it's too late. Abaddon took over Heather's body once more.
In Darkness, Kate uses the Mother Earth sigil to try and strip Cassie of her magic.
It seems the sigil Amelia used was meant to prevent people from being overtaken by Demons and using their vessels as a way to bring chaos, without killing the host of the Demon. The disadvantage of the sigil is it doesn't kill the Demon, and places the host into a catatonic state.
Malleus Maleficarum: Hammer of the Witches
This sigil that Jane used was meant to paralyse a witch and his powers. It must be carved on the bottom of a chair. When the witch is on the chair, someone has to activate it with a cristal.