$ gpg --keyserver hkps://keys.openpgp.org --recv-keys A9AB5AB778FA5C3522FD0378F82F4B16DEC408F8
In case of problem, the GPG key can be downloaded here:
Release signing key (format: PGP public key).
$ gpg --edit-key A9AB5AB778FA5C3522FD0378F82F4B16DEC408F8
gpg> trust
$ gpg --verify weechat-4.4.4.tar.xz.asc weechat-4.4.4.tar.xz
gpg: Signature made Sat 20 Oct 2012 07:36:35 PM CEST using RSA key ID DEC408F8
gpg: Good signature from "WeeChat (signing key) <webmaster@weechat.org>"