The serial is stored in the art partition in the flash.
You can read it using this command: art=$(cat /proc/mtd | awk -F: ‘/art/{print $1}’) && dd if=/dev/$art bs=1 skip=$((0x30)) count=16 2>/dev/null && echo
art=$(cat /proc/mtd | awk -F: ‘/art/{print $1}’) && dd if=/dev/$art bs=1 skip=$((0x30)) count=16 2>/dev/null && echo