You should be able to install your Privyseal and hyperlink it to your Certificate by using the links provided by your Certificate Issuer.
Ensure you select the HTML option in your email signature editor.
Menu > Preferences > Account Settings > Signature text > (tick "Use HTML" box) > (paste the HTML below into the box) > Ok
You should now test to see if your Privyseal is properly installed by composing a new email and seeing if your Privyseal is pulled into your new email with the current date and time. If it is properly installed, your Privyseal should always reflect the current date and time, as your Privyseal's details are checked every minute.
(If your Privyseal disappears you should check with your Certificate Issuer. Your Privyseal serves as an easy way to tell that everything is in order, or that there is a problem you may need to attend to.)