From Knitting Lingerie Style:
Makers of early machine-knitted hosiery faced a technical difficulty: The foot and the leg, usually made separately, required an obvious and unsightly seam when joined. Stocking-makers would cleverly disguise this seam by embroidering over and around it, thereby turning a "defect" into an attractive embellishment. During the 16th and 17th centuries, clock faces were the most popular motifs for this purpose, so much that so even when a different motif was used to hide the seam, such as flowers or fans, it was still called a clock.
These stockings feature a panel of traditional feather-and-fan stitch down the fronts and backs, and a pretty embroidered feather and fan at the ankle, where clocks originally appeared. Not only is this stitch pretty, but it’s an authentic motif. Fans were, after all, an accoutrement of lady’s attire once used for flirting with and attracting men. And feather quill pins were used to write secret love notes to the object of one’s affection.