Why did ladies draw lines on there legs in world war 2?

Nylon was a valued material so the development of nylon stockings was stopped. Before the war, stockings were made with a seam running down the back, where the two halves of the nylon were attached together to form the stocking. The seam unintentionally emphasized the curve and shape of the leg, so when women could not wear stockings, they reproduced the "seam" often using eyeliner.