Talk:Character Table/@comment-24860891-20140701154358/@comment-4509370-20141215185010

A double circle is commonly used in Japanese to represent excellent work, or 'well done!'. You can find details about it for example here and here, so they were probably going for the full set of ◎○△×.

(Incidentally, this system is also why ○ is used to Confirm and × is used to Cancel on Japanese Playstations.)