I wondered that. This issue https://github.com/source-foundry/Hack/issues/1 https://github.com/source-foundry/Hack/issues/1 points to https://github.com/powerli

I wondered that. This issue https://github.com/source-foundry/Hack/issues/1 https://github.com/source-foundry/Hack/issues/1 points to https://github.com/powerline/powerline https://github.com/powerline/powerline which appears to be some kind of status-line plugin thingy for Vim that uses certain glyphs for arrows and things. I haven't yet managed to find out which glyphs.