Google Trends lists Harley Quinn as the most searched for Hallowe'en costume.
Which may be why DC Comics has registered Harley Quinn, along with Poison Icy and Wonder Woman for
Clothing for men, women and children, namely, shirts, t-shirts, sweatshirts, jogging suits, trousers, pants, shorts, tank tops, rainwear, cloth baby bibs, skirts, blouses, dresses, suspenders, sweaters, jackets, coats, raincoats, snow suits, ties, robes, hats, caps, sunvisors, gloves, belts, scarves, sleepwear, pajamas, lingerie, underwear, boots, shoes, sneakers, sandals, socks, booties, slipper socks, swimwear and masquerade and Halloween costumes and masks sold in connection therewith
Looks like they have all their bases covered. And whoever sold these costumes should watch out!