Turn off XML UTF-8 in All Walk Settings. That setting, when enabled, replaces hi-bit characters in the range U+0080 to U+00FF with a question mark, since they are not valid in some versions of XML and some XML engines will produce an error. In HTML they are accepted.
The problem is not that it's a question mark. the issue is that if we have a symbol then the user will have to enter that to get those search results. Better to take the copyright and the registered trademark and strip them because they only are needed for customer viewing.