The logos are being loaded via http://upload.wikimedia.org using CSS such as
<div class="portlet" id="p-logo">
<a style="background-image: url(http://upload.wikimedia.org/wikipedia/en/b/bc/Wiki.png);" href="/wikipedia/en/wiki/Main_Page" title="Visit the main page [z]" accesskey="z"></a>
</div>
When accessed via the secure.wikimedia.org site with Internet Explorer 7, it results in a blocking warning "This page contains both secure and nonsecure items", which needs to be turned off.
Turning off this warning involves going to Tools -> Internet Options -> Security tab -> Internet zone -> Custom level -> Miscellaneous section -> "Display mixed content" = Enabled.
Version: unspecified
Severity: normal