Opera

If Opera does not show a closed padlock icon to indicate that a page is secure even though you are on a HTTPS server, the cause is usually that you have come to the secure page through a link to a non-secure (HTTP) URL which is redirected to a secure (HTTPS) URL. Since part of the transfer was not secure, Opera will consider the connection as not secure. A reload of the secure page will show the correct status.

Another possibility is that important parts of the page are linked to HTTP (non-secure) elements, in which case the site's administrator should probably consider linking to elements on a secure site instead.