A question about arcade mode rating

When viewing the arcade mode scoreboard, the column farthest to the right states a given player's "rating" for a particular level and difficulty. The rating is usually a medal one managed to achieve (bronze / silver / gold). However, I noticed some people have a symbol which looks like a rune stone instead of a typical medal. My question is: how to obtain this symbol? Do any specific requirements have to be met (like: kill all enemies on the level)? Or is it simply about going past a certain threshold of points?

Oh, THIS symbol??



My guess is that it was done on Ultra Nightmare, but I'm not sure.

get all of the runes stones, I dont know if its quickly as I'v not gotten the red one yet, my game keeps crashing. (edit) oh bad ass job ling, way to go man.

actually I found out its just a hidden score medal, just the next step up from gold. You need to score very well.

It's pretty horrifying to see Norton Antivirus beating 99% of the playerbase.