Add editorial note to Redirect page above Why Join content

Editorial would like to include a note about why a user might be seeing the redirect page above the Why Join content. For 1.8.5, we added the content to the Why Join page, but since it's possible to link to Why Join separately, we'd rather have it appear only in the context of a re-direct.

What would be the best way to do this? Add a trans key? Add a new page that is included similarly to Why Join on the Redirect page?