See also related Post: https://davidring.ie/2019/09/18/vxrail-lookup-model-psnt/
In addition to the physical tag at the front of the VxRail appliance you may also leverage PowerCLI, ESXi console or vCenter GUI to pull the ST/SN of each VxRail appliance.
Get-Hosts -Server VxRailManager_IP -Username firstname.lastname@example.org -Password PW |ft sn, hostname
Per individual host:
/opt/vxrail/tools/ipmitool fru print 17
With the benefit of the VxRail vCenter Plugin we can reference several pieces of useful info related to hosts including SERIAL Numbers: