The Benediction Sign is mistakenly called an Ulnar nerve injury. It is in fact a MEDIAN nerve injury at the level of the Elbow.
It occurs as the median nerve supplies the lumbricals 1 and 2, which flex the the first 2 digits at the metacarpophalangeal joints. Another way to test this is to ask the patient to make a fist. With a Median nerve injury they will not be able to and the index finger will stick up. Also review the examination of the hand.
You can also ask the patient to make the sign of an ‘o’ with the thumb and the index finger. In a Median nerve injury it will be more of a pinching motion than a smooth ‘o’