Comment 18 for bug 730225

Just trash it using dd. Flexnet should be rewriting a new copy of signature in a new place next time related application runs.
Or you can do the following workaround:
cat /boot/grub/lnxboot.img /boot/grub/core.img > /somewhere_you_have_write_access/grldr
then copy the file to a Windows partition add a corresponding item to boot.ini (might not work) or bcd (verified by myself) that points to grldr and
dpkg-reconfigure grub-pc
when prompted to select on which disk or partition will grub be installed on, uncheck the disk (i.e./dev/sda) but check the partition (i.e. /dev/sda4 or so) on which you install Ubuntu.
By doing all those above, you'll let Windows boot managers take over Ubuntu's. But remember, when you encounter with "grub" and "grub-pc" software package updates in Ubuntu, it's suggested to re-generate grldr afterwards.