Currently, the Symantec Endpoint Protection client for macOS systems does not include the serial number of the endpoint in the client metadata that is collected and submitted to the Symantec Endpoint Protection Manager.
The Symantec Endpoint Protection client was never updated to collect the endpoint Serial Number from a macOS endpoint.
macOS Operating System
Symantec Endpoint Protection 14.x
At this time, there is no option that is customer configurable to include this information in the client metadata that is collected by the SEP client, and sent to the SEPM.