@SERIAL[d:]: Returns the serial number of the specified disk drive (in hex, i.e.: ABCD:0123). The drive letter must be followed by a colon.
If the argument is a partial filename without a drive, @SERIAL will expand the filename to get the drive.
Examples:
echo %@serial[C:]
1B:EB6D
echo %@serial[%_disk:]
F82B:746
See also: @LABEL.