On the bottom of question pages is a prompt to "Sign up or login":
But login is a noun and log in is the verb.
See http://loginisnotaverb.com/ and "log in to" or "log into" or "login to".
The prompt should use verbs: "Sign up or log in".
(If you click the "log in" link, the next page uses "log in" and "login" correctly.)