Hard Drive info VBS using Win32_DiskDrive - what is "Signature" ?

Hi Experts

I'm not terribly well acquainted with either VB Scripting or WMI, but I participated recently in another question about creating backups on an external usb hard drive using "DOS" batch and xcopy, and the subject came around logically to performing some checks to ensure that the drive letter was assigned to the correct drive.  The suggestions were to use the Volume Label for the check, but it got me thinking about the Manufacturer's Serial Number as an even more accurate check.

There is the Volume Serial number of drives, which is assigned by the operating system, but that wouldn't be applicable if the drive was connected to another PC, but the manufacturer's serial number for the hard drive would remain static if it can be retrieved.

I discovered a couple of VB scripts that use the "Win32_DiskDrive" class and retrieve the "Signature" value for drives.  I am wondering what this value actually is.

Here's the details I have gathered in respect of my two internal IDE hard drives and my external USB hard drive using Windows commands, AIDA32 (now Everest), Belarc Advisor, and the VBS file in the code snippet.

Seagate (C:) One Partition - System Drive.
WMI Signature: 281022655 <-------------------------------- **
Aida32 and Belarc Model ID: ST340016A
Aida32 and Belarc Serial No: 3HS96FM0
Volume Label: CCB6-7A61 (or CCB77A61 MSINFO32)

Maxtor (D: NTFS and E: FAT32)
WMI Signature: -1297841220 <----------------------------- **
Aida32 and Belarc Model ID: Maxtor 6L160P0
Aida32 and Belarc Serial No: L41C7NTH
Volume Serial D: 7C77-844F (or 7C77844F MSINFO32)
Volume Label D: XP_NTFS
Volume Serial E: 0B66-1ED8 (or 0B661ED8 MSINFO32)
Volume Label E: STORAGE

Freecom USB (I: J: K:) 3 Partitions all FAT32
WMI Signature: 50627703 <----------------------------- **
NirSoft USBDeview Serial No: DEF10B39A73D
NirSoft USBDeview Device Name: Classic SL Hard Drive
Model ID: Freecom HDS72808 0PLAT20
Volume Serial I: 9451-248B (or 9451248B MSINFO32)
Volume Label I: FREECOM1
Volume Serial J: D827-A03B (or D827A03B MSINFO32)
Volume Label J: FREECOM2

Can someone tell me what Signature is, and where it is retrieved from?

Thank you
Bill

VBS file below.  I'm running this in Windows XP SP3.

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On Error Resume Next
 
Const wbemFlagReturnImmediately = &h10
Const wbemFlagForwardOnly = &h20
 
strComputer = "."
Set objWMIService = GetObject("winmgmts:" & "{impersonationLevel=impersonate}!\\" & strComputer & "\root\cimv2")
Set colItems = objWMIService.ExecQuery("Select * from Win32_DiskDrive", "WQL", wbemFlagReturnImmediately + wbemFlagForwardOnly)
 
For Each objItem In colItems
    WScript.Echo "Caption: " & objItem.Caption
    'WScript.Echo "Model: " & objItem.Model
    WScript.Echo "MediaType: " & objItem.MediaType
    WScript.Echo "Manufacturer: " & objItem.Manufacturer
    WScript.Echo "MediaLoaded: " & objItem.MediaLoaded
    WScript.Echo "InterfaceType: " & objItem.InterfaceType
    WScript.Echo "Description: " & objItem.Description
    WScript.Echo "DeviceID: " & objItem.DeviceID
    WScript.Echo "Name: " & objItem.Name
    WScript.Echo "Index: " & objItem.Index
    WScript.Echo "Partitions: " & objItem.Partitions
    WScript.Echo "Status: " & objItem.Status
    WScript.Echo "Signature: " & objItem.Signature
    WScript.Echo
Next