This design comes to us through a rare old manuscript called "The Book of Magical Talismans." This "Signet" is shown on page 31 but aside from the drawing of the Magical Design and the inscription "Signet For Gaining Help Of Good Spirits," there is no explanation of the names or symbols that compose the design.
One can recognize the names of Archangels forming a protective circle around an inner design consisting of the names or initials of Various Angels as well as several "Sealing Taus" i.e. Crosses of Protection. [The Tau Cross is named after the Greek letter that it resembles.]
The other symbols remain a mystery.