Thanks for reporting this - turns out that when the latest ISO point releases were made for 16.04 that while the various SUMS files were updated, the corresponding .gpg signature files were not regenerated. This has now been done.
Thanks for reporting this - turns out that when the latest ISO point releases were made for 16.04 that while the various SUMS files were updated, the corresponding .gpg signature files were not regenerated. This has now been done.