27 CFR 19.189: Identification of structures, areas, apparatus, and equipment.

(a) Buildings. The proprietor must mark each building at a distilled spirits plant where spirits, denatured spirits, articles, wine, or distilling or fermenting materials are kept with a distinguishing number or letter.

(b) Tanks. The proprietor must mark each tank or receptacle for spirits, denatured spirits, or wine to show a unique serial number and capacity.

(c) Stills. The proprietor must number and mark to show the use of each still, fermenter, cooker, and yeast tank.

(d) Other major equipment. The proprietor must identify the use of all other major equipment used for processing or containing spirits, denatured spirits, wine, distilling or fermenting material, and all other tanks, unless the intended purpose is readily apparent.