27 CFR § 26.40 - Marking containers of distilled spirits.
The distiller, rectifier, or bottler shall serially number each case, barrel, cask, or similar container of distilled spirits filled for shipment to the United States. In addition to the serial number of the container, the distiller, rectifier, or bottler shall plainly print, stamp, or stencil with durable coloring material, in letters and figures not less than one-half inch high, on the head of each barrel, cask or similar container or on one side of each case, as follows:
(b) The brand name and kind of liquor;
(c) The wine and proof gallon contents; or, for bottles filled according to the metric standards of fill prescribed by § 5.47a, of this chapter, the contents in liters and the proof of the spirits; and
(d) In the case of barrels or casks, the serial number of the permit to ship, Form 487-B, prefixed by the number of such form (e.g., “487-B-61-1”)
(e) In the case of bulk containers shipped to the United States under subpart Ib, the serial number of the application and permit to ship, TTB Form 5110.31, instead of the serial number of Form 487-B.