This read-only variable-length string reports the serial number of a physical assembly, unique across customer-orderable entities though it may be shared by multiple assemblies of the same type; an empty string is returned if the entity has no serial number. Admins use it for asset tracking and warranty or RMA purposes when identifying a specific physical card. For example, an admin filing a hardware RMA would read this object to obtain the exact serial number needed by the vendor's support process.