I believe this could be an Undocument Mark comprised of the katakana letter 'Hi' ヒ.

Although this mark could be a broken Kita 北, because of the distinct bold form of the symbol and way it's center without any lind of distortions I feel that it's not a Kita mark.

This light green float measures about 48 inches in circumference, so it's about 15 1/2 inches in diameter.