GitHub icons missing
github, icons
Solution
These icons are done with the font - 'Octicons Regular', so that won't be loading for you for some reason. It is all done with CSS so shouldn't require js to work. See this page for details:
https://github.com/styleguide/css/7.0
Perhaps try checking that you don't have remote font loading disabled (there is a command line switch I think), or a bad version of this font cached, or some other font issue - you can check what has loaded if you enable the inspector and look in resources for that frame, there should be a Fonts listing with the Octicons font listed. You could also try downloading the font and installing locally.
If you cannot load other fonts, probably it's a setting rather than this specific font.
You might be able to see the font loading settings here:
chrome://about
I think the setting you need is
--enable-remote-fonts
which you can run from the command line to turn them on again (on by default now).
Problem
Is anybody else's GitHub missing icons? There are no JS errors, and from what I can tell looking at `resources` in Chrome developer tools, no 404 errors.