Being very active on skepitcs.se last week, I realized this site gets too many unreferenced answers, this will cause answers to get deleted or make the moderators comment on the answer and asking the answerer to reference their answer (waste of time, waste of energy).
Usually, google links to one of skeptics.se's questions and new users sign up (you can see that with their 1 reputation) and post an answer.
Most of new users don't check any FAQ pages nor they know that this site has some strict rules for answers.
I think it would be productive to tell the answerer (new members only) to reference their answer.
Adding a banner above the answer box sounds like a good practice: