.com/theme/templates/github.html

{% if article|default(False) %}

    <a href="{{ article.gh|default(GITHUB_URL) }}" class='github'>
        <img style="position: absolute; top: 0; right: 0; border: 0;" src="http://s3.amazonaws.com/github/ribbons/forkme_right_darkblue_121621.png" alt="Fork me on GitHub" />
    </a>

{% elif GITHUB_URL %}

    <a href="{{ GITHUB_URL }}" class='github'>
        <img style="position: absolute; top: 0; right: 0; border: 0;" src="http://s3.amazonaws.com/github/ribbons/forkme_right_darkblue_121621.png" alt="Fork me on GitHub" />
    </a>

{% endif %}