There is a signature hand position used in aikido and jujutsu that practitioners often call the "pistol grip" because your hand assumes the shape of a pistol. The index finger is extended while the other three fingers are curled halfway in. The thumb is typically extended away from the palm in a gripping position.
This hand position is known to karate as ippon ken, the "one-point fist." Traditional senseis tell us that we are poking someone in the chest with the tip of our index finger. In the grappling arts, this hand position means that we have grabbed someone by the hand and are about to apply a painful wristlock. Here are two examples.
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Jujutsu artists make use of many "poking" techniques (atemi waza), but not typically with the tip of the index finger. That finger is always kept extended for the purpose of channeling ki. It is very unlikely that the ippon ken postures in the Shotokan katas are poking at anything.
Tom Frobel tells me that the term "pistol grip" sometimes means a clenched fist that grips the cloth at a person's wrist. These photos will serve to explain my meaning.