The plantar sign means that the big toe is involuntarily bent up or down when the little toe side of the sole of the foot, from the heel to the little toe, is pain-stimulated to a moderate degree.
If the big toe bends downwards, the toe is "pinched together", the plantar sign is normal and is indicated as negative.
If the big toe is bent upwards, the toe "sprawls/stretches up", the plantar sign is abnormal and is indicated as positive.
"Positive Babinski" speaks very strongly for an injury to the pyramid course, but not if the person is younger than 1 year old or severely intoxicated.