The AssetId property is a user writable alphanumeric character sequence uniquely identifying a component. The ID is provided by the vendor, integrator or user of the device. It contains typically an identifier in a branch, use case or user specific naming scheme.
This could be for example a reference to an electric scheme. For electric schemes typically EN 81346-2 is used.
The AssetID of the AxisType provides a manufacturer-specific axis identifier within the control system.
This property is defined by ComponentType defined in OPC UA DI.