Of course, that's it. Users copy-paste from a wrong character set. Didn't think about that.
Here's a quick regular expression that will take care of that for you:
\u00AE is the "circle r"
® is the corresponding HTML entity ( = ® )
I'm not sure if you use PHP/ASP/Perl/whatever, but I'm sure your programming language of choice has some way to implement a RegExp