Circles of Power give Geralt a buff for 5 minutes and are stackable up to all 5 circles. They appear as a faint shimmer when they are not activated by the medallion, and show up as bright red aura after being activated by the medallion, using . The Witcher medallion glows and emits a distinct sound when Geralt is within the Circles of Power.
Circle Name
Symbol
Effect
Endurance
Shield
Armor +20%
Life
Cross
Vitality regeneration +2 / Vitality regeneration in combat +1
Power
Triangle
Sign intensity +20%
Vigor
Hexagon
Vigor regeneration +2 / Vigor regeneration in combat +1
[Possible bug] Circle of Vigor has the same effect as Circle of Life. While stacking Circle of Life and Circle of Vigor, only one of the effect is being taken into account. Upon expiry of that Circle's effect, the other Circle's effect won't be taken into account despite still being active.
There are also Circles of Power to enhance a single sign for 5 minutes. One of these is in Flotsam forests, and enhances the Quen sign. Another one, for Aard Sign is outside Loc Muinne.