What does a unicorn image on Github.com mean?

This is the Unicorn logo, which is a way to host Rails projects. Remember mongrel_rails? It's like that but much, much faster.

When GitHub comes back online, you can see the Unicorn project here.

It means that github is down for some reason.

It means GitHub is down. It means you can't use GitHub any more. See https://status.github.com/.

I guess you can bask in the unicorn's glory or something? Other than that, you can do pretty much whatever you like.

One thing that also isn't down is https://developer.github.com/.

Search for it in Google and check any of the link. Looks like that's the icon shown only when the site is down (or) the resource not found etc...

For example: check think link

https://github.com/defunkt/unicorn