Iianm, that icon only appears if there are unencrypted content on the page that you're viewing. Was it Chrome? The other browser vendors use different and less disturbing or troubling methods to indicate unencrypted content.

Unencrypted content in your encrypted HTML page is an impossible problem to solve for a forum if you want to allow your users to use external images that comes from sites without HTTPS (eg: signature images, photographs, hardware charts, etc) or don't have the technical expertise to know that they need to use HTTPS sources instead of unencrypted sources.

Actually chrome will show a yellow icon if images are loaded from http:// sites.

The crossed padlock is due to our use of http:// scripts from our advertising providers, which don't have HTTPS support. We're out of luck here, because we do need the ads to be shown. But if you use IE9, it will conveniently avoid them

Sorry, we can't make it green. But I assure you that your browsing with https:// is at worst as secure as http://