UTF-8/Non UTF-8

Helping out a friend with Quality Control on their forum...

this:  is displayed in some of the posts. Most if not all of them are old posts and apparently were made before they switched forum software.

From what I was told this is when non-utf-8 characters got translated to utf-8. Is there a way to translate this back (just for curiosity's sake). Near as I can tell they are not impacting the posts and don't seem to be anything missing other than possibly spaces or some special character.

I haven't been able to find a way to convert.. using my own software or by googling.

Thanks!