25 CFR §310.4

All marks shall be applied to the article with a rubber stamp to be furnished by the Indian Arts and Crafts Board. Each stamp shall bear a distinctive letter and may be used only by the person to whom it has been issued. With the addition of the distinctive letter, each stamp shall read: On baskets and fabrics which offer no surface for the application of such a rubber stamp, the stamp shall be placed on a paper tag attached to the article by a wire caught in a lead seal disc that shall be impressed and made fast with a hand seal press furnished by the Indian Arts and Crafts Board.