If you are using a Debian based distribution (including Ubuntu & Mint), you can disable the gpg agent part of Gnome Keyring on a system-wide basis using the following command:

$ sudo dpkg-divert --local --rename --divert /etc/xdg/autostart/gnome-keyring-gpg.desktop-disable --add /etc/xdg/autostart/gnome-keyring-gpg.desktop

If you later decide to reenable it, then you can use:

$ sudo dpkg-divert --rename --remove /etc/xdg/autostart/gnome-keyring-gpg.desktop