Please consider putting some text at the top of home page saying these 4 ways are the only ways to sign up.
There is no on-site registration form.
Change the label from “alternative” to something like “the ONLY available login methods…”

All I noticed was the “alternative login” - for facebook, google, twitter (having none of those) & what I was sure must be Hello, Kitty. I’ve never noticed the pre-pubescent girlish kitty icon for Github - all the yrs I’ve used the site. :)

I tried to make some hidden registration form display, near the word “Login.”
The page source shows there’s nothing else there.

I finally found a blurb under Announcements - how to sign up.

Thanks.