Board Thread:General Discussion/@comment-1321146-20140215105002/@comment-5007040-20140215121422

Tupka217 wrote: And for that, the stupid triangles would have to go. What do those mean, anyway? That they've risen in the ranks? That they've got a new badge? Plenty of these haven't edited in quite a while, but still get a triangle.

It's for rising on the ranking, you can read that on this page: Help:Leaderboard.