Reproduced on mw.org: https://www.mediawiki.org/wiki/Special:UserLogin
The logo at the top left side is missing. It is visible on all other pages.
Version: 1.25-git
Severity: normal
URL: https://www.mediawiki.org/wiki/Special:UserLogin
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=56257