15 U.S. Code § 1174 - Labeling and marking of shipping packages
All gambling devices, and all packages containing any such, when shipped or transported shall be plainly and clearly labeled or marked so that the name and address of the shipper and of the consignee, and the nature of the article or the contents of the package may be readily ascertained on an inspection of the outside of the article or package.
Source(Jan. 2, 1951, ch. 1194, § 4,64 Stat. 1135.)