The contributors license their work with a creative commons license and more specifically "cc by-sa". This means that the if anybody, e.g. SE, wants to use the work of a contributor then they need to provide the (original) license with the works (or at least one that is not restricting the previous, but that is another issue).
Full site footer:
On the regular website this is done by making notice of this license with a link at the bottom of the page.
This seems to be to save space on the small screens, but is it reasonable and correct?