You have the three tabs (Primary, Elder Scrolls Online and Guild Wars 2)
While you are in Primary, where it says "Selected Signature". It has a button under the signature, or if it is not created yet, under the text "Signatures may take up to 24 hours to build. This button says "Set this as My Gaiscioch Site Signature", click that button.
Then go up under the current Gaiscioch Site Signature and click "Save Signature". Now go to a forum post that you wrote and verify that it is set. note that if it is not created yet, nothing will show up.
When you have verified that you can at least set it to the default, then you can start customizing it.