The top banner used to be settable; we have used it before. Not sure if that is still the case. I agree that is the best option.

FWIW, I did get back clarification from Atlassian about the 2 issues being developed:

The first is for the utility of the "Contact Administrators" message - I've left a comment for the developer letting him know what the issue is you're having and he is looking into filing a public facing report for that. I'm still following up with the other, but it's regarding CAPTCHA control for the public signup.