Comment by mananaysiempre

GitHub actually can natively mark a repo as a mirror (or could? I can’t find an example now, but they have always been rare). The book-with-bookmark icon before “user / repo” in the page header is replaced by a mirror-and-reflection-ish–looking thing, and the badge after it changes from “Public” to “Public mirror”. Unfortunately, forcing you into “social coding” (wait, is that no longer on the homepage?) takes priority, so that mark can only be given out by GitHub staff through manual intervention, and it doesn’t often happen.