Sigil

A Sigil (シジル) is a magic symbol used to represent certain subjects according to Idol Theory. Most often in Western magic it represents an angel.

Principles
Sigils represent things from a special cross, to that of Hebrew alphabets. The lines used in a sigil are used to display a word. However, it is most often used to display a name of an angel in order to obtain Telesma. What the sigil draws out depends on the angel the sigil represents, like Archangel Gabriel representing the direction of south, which the spellcaster may use to tell others which direction to go.

What they represent seem to imply that they can also be used in magic circles, for when writing the name of the angel whom the spellcaster desires to borrow the from, among other functions, instead of regular alphabets.

As Silvia demonstrates, there is no reason for a sigil to be solely written on paper or on the ground - they can also be formed through various movements, like using a rope to signify the sigil of Archangel Gabriel.