The "Fork me on GitHub" ribbons supplied by GitHub are cute but they have a few issues: they mean having to load an extra image and they overlap the content of the page on smaller screens.
Instead of using an image it is totally fine to use CSS for the same purpose. This is an example of a imageless ribbon that falls back to an inline link when there is not enough space. If you see this on a screen less than 800 pixels there should be a link above, if you have a wider screen the ribbon should be up in the corner.