An arcane rune or sigil is a thing of great power sometimes in the form of runic circles for rituals and transference of power.
Arcane runes provide a way of magic to elevate beyond what even an experienced mage can handle. They bring objects of magic into the reach of common folk and give some mages the power to peer beyond the limits that reality would set upon them.
Arcane runes can also be seen as stones or symbols of power if the power is put into the symbol or object rather then a circle.