559.03 Declared face value; redemption.—No trading stamp company shall distribute trading stamps in this state or shall redeem trading stamps hereafter issued therein unless each stamp has legibly printed upon its face in cents or any fraction thereof a cash value determined by the company, and the rightful holders may, at their option, redeem the stamps in cash when duly presented to the company for redemption in a number having an aggregate cash value of not less than 25 cents.