The black square is unfortunately placed over the woman's shingle bob cut on Godwin's cover, so that the nape of her neck is not exposed. This would be like seeing a black bar placed over a woman's side-boob on a modern magazine cover, I think. The shingle bob cut exposes the nape of a woman's neck--which men rarely got to see in generations previous (unless they were in flagrante delicto)--and thus I believe it was a new erotic zone in the '20s, apt to stir up interest from both male and female readers.
This is from a web article on "The Bob" by Michael Warner:
. . . Tears and smelling salts accompanied the sacrifice as shorn cascades of crowning glories tumbled to the floors of barbershops. Men raged over the female invasion of the barbershop but at that time, the-cutting-of-hair was still a male-dominated occupation. In some cities, long lines of women were reported standing outside barbershops while inside, many women patiently sat on floors waiting their turn to be bobbed. In New York City, reports of up to 2,000 heads per day were being clipped.
Overseas, it was reported that while King George took no official position to the controversy of bobbed hair, her majesty, Queen Mary, preferred if ladies with short hair would in some way conceal that fact at court functions or royal ceremonies. Hair additions . . . were commonly used to conceal the shingled back. Many women actually saved their long locks just so they could use them to conceal their new haircut!
. . . The shingle or the "boyish bob" introduced in 1923 featured hair which tapered into a V-shape at the nape of the neck with either waves or spit curls at the sides.