Do you know about this functionality in SAP TM.
ISO 6346 is an international standard covering the coding, identification and marking of intermodal (shipping) containers used within containerized intermodal freight transport by the International Organization for Standardization
Refer to; ISO 6346 - Wikipedia
This functionality supports you to ensure the Container Number insert in field Container/Registration Number is correct.
In case the number is not correct a Warning will appear:

If the Number is correct no Warning will appear.

To active it in SAP TM you need to follow this step:
Go to SPRO:

Once it’s open select the TU Group you’re using and in the Resource Class Select number 10 Container and save it.

With these steps the validation will be active for a user to get the validation of the ISO 6346
Technically SAP is using this Method /SCMTMS/CL_COMMON_BO_HELPER-CHECK_CONTAINER_ID
Refer to:
2737247 - TM: No check on container ID based on ISO 6346 - SAP for Me
Transportation Unit Resource | SAP Help Portal
Parameter Description | SAP Help Portal
Hope that can help you.
Thank you and regards!
Rogerio Lima.