27 C.F.R. § 24.168
(b) Tank markings.
(c) Puncheon and barrel markings. Puncheons and barrels, or similar bulk containers over 100 gallons capacity, will be marked in the same manner as tanks. A permanent serial number need not be marked on puncheons and barrels, or similar bulk containers of 100 gallons capacity or less, used for storage, but the capacity must be permanently marked.
(Sec. 201, Pub. L. 85-859, 72 Stat. 1378, as amended, 1379, as amended (26 U.S.C. 5352, 5357))
(Approved by the Office of Management and Budget under control number 1512-0503)
[T.D. ATF-299, 55 FR 24989, June 19, 1990, as amended by T.D. TTB-91, 76 FR 5478, Feb. 1, 2011]