I believe the hair forum and a couple other forums are public but others like the makeup forum, entertainment, etc are private and you can’t view unless you have a membership
There is a member who added in their signature, an image from another site using *http://* not *https://*. This is why you see that message.
If you are on a computer you can inspect the relevant thread (Chrome menu, Firefox etc) and then click the Network tab and refresh the page. You will see the resources that load under http.