This number is the “tracking number” of the unit. It is made up of the prefix (owner code + product group code), registration number and check digit. This number can be found on all four sides of the container, the roof, inside panels and on the CSC plate.

The owner code consisting of 3 capital letters must be unique and registered with the International Container Bureau (BIC). If absent, the container cannot be identified. Check the owner code HERE
A product group code consisting of one capital letter U, J or Z (U – for all freight containers // J – for detachable freight container equipment // Z – for trailers and chassis)
A registration number (or serial number) consisting of only 6 digits.
The check digit always consists of a single-digit number and is highlighted in a box. This is to verify the owner code, product group code and registration number were accurately transferred. No container number will be accepted in a data processing system if the check digit does not match. This was built in to ensure that a number of transmission errors cannot cancel one another out.