A SIM card is uniquely identified by its ICCID (serial number). SIM management systems (eg Jasper) will allow you to search for a SIM using this.

Wikipedia link

There are two places that this information is shown in our systems:

OEM Server:

Click on the 'Details' link for the device:

On the details page the SIM ICCID is shown:

Telematics Guru

You can find the SIM ICCID on the 'Advanced' tab of the Asset.

This column is now also available on the "Asset List" report.