USB Device viewerで確認

マイクロソフトのUVCview.x86.exeを使い、2番目に接続したUSBデバイスの情報を確認したのが以下になります。
この結果を参照すると、iSerialNumber の値がレジストリキーの値として利用されていることがわかります。

---===>Device Information<===---
English product name: "USB Flash Disk"

ConnectionStatus:
Current Config Value: 0x01 -> Device Bus Speed: High
Device Address: 0x01
Open Pipes: 2

===>Endpoint Descriptor<===
bLength: 0x07
bDescriptorType: 0x05
bEndpointAddress: 0x81 -> Direction: IN - EndpointID: 1
bmAttributes: 0x02 -> Bulk Transfer Type
wMaxPacketSize: 0x0200 = 0x200 max bytes
bInterval: 0xFF

===>Endpoint Descriptor<===
bLength: 0x07
bDescriptorType: 0x05
bEndpointAddress: 0x02 -> Direction: OUT - EndpointID: 2
bmAttributes: 0x02 -> Bulk Transfer Type
wMaxPacketSize: 0x0200 = 0x200 max bytes
bInterval: 0xFF

===>Device Descriptor<===
bLength: 0x12
bDescriptorType: 0x01
bcdUSB: 0x0200
bDeviceClass: 0x00 -> This is an Interface Class Defined Device
bDeviceSubClass: 0x00
bDeviceProtocol: 0x00
bMaxPacketSize0: 0x40 = (64) Bytes
idVendor: 0x0411 = BUFFALO INC.
idProduct: 0x0098
bcdDevice: 0x4000
iManufacturer: 0x01
English (United States) "BUFFALO"
iProduct: 0x02
English (United States) "USB Flash Disk"
iSerialNumber: 0x03
English (United States) "B020000000141320"
bNumConfigurations: 0x01

===>Configuration Descriptor<===
bLength: 0x09
bDescriptorType: 0x02
wTotalLength: 0x0020 -> Validated
bNumInterfaces: 0x01
bConfigurationValue: 0x01
iConfiguration: 0x00
bmAttributes: 0x80 -> Bus Powered
MaxPower: 0x64 = 200 mA

===>Interface Descriptor<===
bLength: 0x09
bDescriptorType: 0x04
bInterfaceNumber: 0x00
bAlternateSetting: 0x00
bNumEndpoints: 0x02
bInterfaceClass: 0x08 -> This is a Mass Storage USB Device Interface Class
bInterfaceSubClass: 0x06
bInterfaceProtocol: 0x50
iInterface: 0x00

===>Endpoint Descriptor<===
bLength: 0x07
bDescriptorType: 0x05
bEndpointAddress: 0x81 -> Direction: IN - EndpointID: 1
bmAttributes: 0x02 -> Bulk Transfer Type
wMaxPacketSize: 0x0200 = 0x200 max bytes
bInterval: 0xFF

===>Endpoint Descriptor<===
bLength: 0x07
bDescriptorType: 0x05
bEndpointAddress: 0x02 -> Direction: OUT - EndpointID: 2
bmAttributes: 0x02 -> Bulk Transfer Type
wMaxPacketSize: 0x0200 = 0x200 max bytes
bInterval: 0xFF