19 CFR 24.13a - Car, compartment, and package seals; and fastenings; standards; acceptance by Customs.
(a) General standards. The seals and fastenings, together, shall
(1) Be strong and durable;
(2) Be capable of being affixed easily and quickly;
(3) Be capable of being checked readily and identified by unique marks (such as a logotype) and numbers;
(4) Not permit removal or undoing without breaking, or tampering without leaving traces;
(5) Not permit use more than once; and
(6) Be made as difficult as possible to copy or counterfeit.
(b) Seal specifications. (1) The shape and size of the seal shall be such that any identifying marks are readily legible.
(2) Each eyelet in a seal shall be of a size corresponding to that of the fastening used, and shall be positioned so that the fastening will be held firmly in place when the seal is closed.
(3) The material used shall be sufficiently strong to prevent accidental breakage, early deterioration (due to weather conditions, chemical action, etc.) or undetectable tampering under normal usage.
(4) The material used shall be selected with reference to the sealing system used.
(c) Fastening specifications. (1) The fastening shall be strong and durable and resistant to weather and corrosion.
(2) The length of the fastening used shall not enable a sealed aperture to be opened or partly opened without the seal or fastening being broken or otherwise showing obvious damage.
(3) The material used shall be selected with reference to the sealing system used.
(d) Identification marks. (1) If the seal is to be purchased and used by U.S. Customs, the seal or fastening, as appropriate, shall be marked to show that it is a U.S. Customs seal by application of the words “U.S. Customs” and a unique identification number on the seal.
(2) If the seal is to be used by private industry (i.e., a shipper, manufacturer, or carrier), it must be clearly and legibly marked with a unique company name (or logotype) and identification number.
(e) Customs acceptance. Seals will be considered as acceptable for use and/or purchase by U.S. Customs as soon as the manufacturer attests that the seals have been tested and meet or exceed the standards provided in paragraphs (a) through (d) of this section, and will continue to be considered acceptable until such time as it is demonstrated that they do not meet the standards. A manufacturer may attest to the qualification of a specific seal, or to an entire product line of seals as of a certain date. Any addition of a seal to a group of seals attested to as a group would require specific acceptance of that seal by Customs.
(f) Testing. All testing of seals deemed necessary before Customs acceptance will be done by the manufacturer or by a private laboratory, and not by Customs. However, Customs reserves the right to test, or to have tested, seals that have been accepted by Customs.
(g) Records. The manufacturer's attestation that a seal meets or exceeds the standards specified in this section and, if deemed necessary by Customs, the seal test record shall be sent to the Assistant Commissioner, Field Operations, Headquarters, U.S. Customs Service, Washington DC 20229.