The Sigillum Dei Aemeth, or Seal of the Truth of God, is most widely known through the writings and artifacts of John Dee, a 16th century occultist and astrologer in the court of Elizabeth I. While the sigil does appear in older texts of which Dee was probably familiar, he was not happy with them and ultimately gained guidance from angels to construct his version.
Dee's PurposeDee inscribed the sigil on circular wax tablets. He would commune via a medium and a "shew-stone" with the angels, and the tablets were used in preparing the ritual space for such communication. One tablet was placed upon a table, and the shew-stone upon the tablet. Four other tablets were placed beneath the legs of the table.
In Popular CultureVersions of the Sigillum Dei Aemeth have been used several times in the show Supernatural as "demon traps." Once a demon stepped within the confines of the sigil, they became unable to leave.