The letter A in sign language (ASL)

A closed fist with the thumb resting upright against the side of the index finger.

Easy to confuse. S crosses the thumb over the front of the curled fingers. T tucks the thumb between the index and middle fingers.

A is one of the six fisted letters - A, E, M, N, S, T - that differ only by where the thumb sits. You cannot check these on yourself, which is what the camera is for.