The disk signature is an unsigned 32 bit number stored in the MBR at offset 1B8h (4 bytes in little endian format).
The disk signature is displayed always in the hex format and not in the decimal format.
In the following screenshot the disk signature is the hex value 64D6E9CD.
The disk signature is created by Windows as a random value when the disk is initialized.
It is important to note that each disk receives a different disk signature and that the disk signature does not change later.
Hence the disk signature can be used to unambiguously identify the respective disk.
Starting with Windows Vista the disk signature is used in the Boot Configuration Database (BCD)
for identifying the respective boot disk.