I would like to add a trademark or registered trademark symbol to my meta description to help carry some company "weight" and to show customers we are the real deal, in contrast to a stalker competitor who plagiarizes the daylights out of my site. The question is, will the use of special characters in my meta description stop Google dead in it's tracks or get my meta tag ignored?
I've seen these characters showing up in the snippets and SERP titles - so they do seem to be OK with Google. That doesn't mean that every search engine will deal with HTML entities properly if they appear in the title or meta description. In fact, historically they haven't.
I believe that technically, there are not supposed to be any special characters in either place. Even the ampersand used to be problematic, but it's part of many company names (like AT&T) that technical accommodations have been made.
I had one case a few years ago where the HTML entity was being displayed "verbatim" so I just pasted in the actual character and that worked fine.