For security reason you have now all the packages signed on obarun repository.
Change your option in /etc/pacman.conf if you want use it like this :

SigLevel = Required DatabaseOptional
LocalFileSigLevel = Optional

[obarun]
SigLevel = PackageRequired
Server = http://www.obarun.org/src/$arch

you can follow the classic wiki on arch about pacman-key (https://wiki.archlinux.org/index.php/Pacman/Package_signing ) to finalize your configuration https://wiki.archlinux.org/index.php/Pacman/Package_signing.

ID-KEY= 7B45DAAC

The next iso release will implement this behaviour automaticly.