For raiders this will show a list of people with the opposite Blasphemy buff, when you are affected by one yourself.
Also, if you are the last pair it will tell you to meet at the middle and say " > Over here < "
For raidleaders there is a separate list weakaura called "officers" which will show you the entire list of people and which debuff they have.
To use the Officer/Raidleader Weakaura simply go to the "Load" tab of that weakaura, and fill in your name in the "Player Name/Realm" box.