7 C.F.R. § 322.32 – Mailed packages.

(a) If you import a restricted article through the mail or through commercial express delivery, you must mark all sides of the outside of that package with the contents of the shipment and the name of the exporting region. The marking must be clearly visible using black letters at least 1 inch in height on a white background.
(b) If you import a restricted article through commercial express delivery, you must provide an accurate description of the complete contents of the shipment for the shipment's delivery manifest entry.
(c) In addition to the export certificate required in § 322.30 (if applicable), a restricted article that is imported by mail or commercial express delivery must be accompanied by an invoice or packing list accurately indicating the complete contents of the shipment.
(Approved by the Office of Management and Budget under control number 0579-0207)