I think he means that this site currently does not have a green padlock in the browser..
My 2 cents. Most times it is a avatar image.
They are the hardest to get cleaned up for me.
Its not a problem with UBBCentral. It is a problem with content on the page that is being linked to. That content happens to be Daryl Fawcett's user avatar, which is being hosted at an insecure web page. Everything else on This page is secure.
The solution here would be to not allow any links from insecure URLs
Control Panel > Features > Require HTTPS for Hotlinked Images
Enabling this feature will only allow hotlinking of images from secure urls (HTTPS) to be displayed inline. Hotlinked images from insecure urls (HTTP) will be presented as a clickable link. When you enable this feature, its recommended that you also rebuild your Posts, Signatures, and Private Messages with the Content Rebuilder, to update their content.
UBBCentral has this option disabled with the intent of being /laxed/. This reasoning is to allow users to easily test out various features of the forum software, such as linking to both HTTPS and HTTP resources.