49 C.F.R. § 179.300-18 – Stamping.

(a) To certify that the tank complies with all specification requirements, each tank shall be plainly and permanently stamped in letters and figures 3/8 inch high into the metal of valve end chime as follows:
1. (1) DOT Specification number.
2. (2) Material and cladding material if any (immediately below the specification number).
3. (3) Owner's or builder's identifying symbol and serial number (immediately below the material identification). The symbol shall be registered with the Bureau of Explosives, duplications are not authorized.
4. (4) Inspector's official mark (immediately below the owner's or builder's symbol).
5. (5) Date of original tank test (month and year, such as 1-64 for January 1964). This should be so placed that dates of subsequent tests may easily be added thereto.
6. (6) Water capacity—0000 pounds.
(b) A copy of the above stamping in letters and figures of the prescribed size stamped on a brass plate secured to one of the tank heads is authorized.