Yellow scarf

When the incarnation of MoogleMB was first created, the "no avatar" icon was a blacked-out image of Protoman, as seen in the game "Mega Man & Bass". It was pointed out that this looked more like one of the Mega Man 8 bosses than Protoman, so Kulock edited the image, returning Protoman's scarf to its normal yellow while leaving the rest black.
While editing, Kulock noticed that the scarf was drawn just right to be placed on the neck of a Kulock sprite, and so his own avatar also wore the scarf. At the same time, the OekakiBBS opened, and unsurprisingly the now scarf-clad Kulock was a popular subject to draw. Kulock expressed concern about every drawing of him now giving him a scarf, and so naturally it became even more common, especially since it helped distinguish him visually from other, lesser moogles.

The No Avatar brandishing the yellow scarf while riding a shark. (Shark_avatars fad.)