19 CFR 12.18: Labels.

Each separate container of such virus, serum, toxin, or analogous product imported is required by the regulations of the Department of Agriculture to bear the true name of the product and the permit number assigned by the Department of Agriculture in the following form: “U.S. Veterinary Permit No. ________,” or an abbreviation thereof authorized by the Animal and Plant Health Inspection Service, Veterinary Services. Each separate container also shall bear a serial number affixed by the manufacturer for identification of the product with the records of preparation thereof, together with a return date.