Fading Suns and Flaming Heresies
Except for occult stigmas, there is no normal way to tell whether someone is or is not using psychic or theurgy powers, unless the power description states otherwise or the occultist himself intentionally betrays it. So, while an oracle consulted by nobles might intentionally reveal her powers, there are no natural signs to reveal whether or not she is faking her omens. Certain powers, such as Wyrd Sight, will reveal the use of occult powers.
Against mental occult powers/rituals (Psyche and Sixth Sense paths, Censure of Guilt rituals, etc.), a target may use his Stoic Mind skill to contest the power. Non-occultists defend with Ego or Faith (whichever is higher) + Stoic Mind, while occultists can choose to defend with their Psi or Theurgy characteristic + Stoic Mind. If the target does not have Stoic Mind, he uses only his characteristic for the roll.
If a target realizes he is being psychically manipulated, he can interrupt the power to contest it. Make sure the psychic keeps track of his goal roll successes; compare them against the target’s roll. Only if the target beats the psychic’s successes is the power canceled; otherwise, it continues for its duration.
A character may ready himself to defend against occult assault with a successful Wits + Focus complementary roll; the victory points are added to the Stoic Mind roll. In this way, someone without the Stoic Mind skill can still defend against occult powers well. “Readying” takes five minutes of meditation and lasts for one span only.
Against physical powers (such as FarHand powers like Crush), the target must use Dodge or try to break the grapple normally (using Strength + Vigor).
Gamemasters should be wary of paranoid player characters who are always trying to defend against psychic powers — whether they are being used or not. With experience, certain people can come to suspect when they are being psychically manipulated, but most people have no clue when it comes to occult activity.