Thread:Project:Support desk/Padlock icons on HTTPS links. Why? and how to switch off?

Does anyone know why MediaWiki puts little padlock icons next to HTTPS links e.g: https://twitter.com/harry_wood

I'm sure the answer is "security" but why? what's this actually guarding against? It used to be a rare thing, but more and more websites these days are switching to be entirely HTTPS (e.g. twitter) It doesn't seem like a particularly significant thing that the user must be aware of when clicking the link. I know there's a security thing around unexpectedly leaving a secure website, but... I would venture to suggest that this padlock decoration is a bit unnecessary these days.

Also what's this feature called (page about it here somewhere?) and how do I switch it off?