27 CFR §44.252

Every package of cigars shall, before withdrawal from the customs warehouse under this subpart, have adequately imprinted thereon, or on a label securely affixed the words “Tax-exempt. For use outside U.S.” or the words “U.S. Tax-exempt. For use outside U.S.”, except where a stamp, sticker, or notice, required by a foreign country or a possession of the United States, which identifies such country or possession, is so imprinted or affixed.