This reminded me of something my mother-in-law would do. As a nurse trained in the 1930s, the bed had to be made perfectly, so she would sew a couple of stitches to mark the center top of her spreads, blankets, and top sheets so she could tell how to always have them centered on the bed when she changed sheets. Then she didn't have to walk around the bed to see if both sides had the exact same amount of drape.