If you're running the currnet build you can edit their profile and click the link on the main page and it'll show a spam check.
The sign up spam detection only detects via email address; my mod at UBBDev detected both IP and EMail address and you'd have to edit the files on server to be able to reattain that functionality.
If you had access to modding files on the server I'd just tell you to have a mod commissioned to not allow usernames and public names to be the same; but users would probably just end up being confused; you could change the language string for the public name to say something like "Please enter your real name"
