I make this suggestion because it's ambiguous to me. When I google/search for answers on SO, I've seen others with (solved) or (fixed) in their titles and navigated to those before others in the results. Why? Because it's a visual cue on google that you otherwise don't get when looking over SO results on google.
I just received a comment from someone after editing my posts' title (Getting Git Hub Comments) to say (solved). Now, I figured I would do so as I had just solved three of my questions in short order. Beyond that, when I went to update the title via my profile, one of my older questions, from march this year also has a (solved) in it.
So that user edited/commented on my post also edited the others that I had just modified by removing the (solved) that I'd just added. No big deal, the user let me know why he decided to edit my posts. But he didn't change the old one. So I have a simple suggestion - just add a quick note into the FAQ about the "answer" system and how it takes priority over anything in the title.
I think we could add it into the FAQ under this section:
https://stackoverflow.com/faq#signatures
Something like, "Remember, the 'mark as answer' system informs viewers if the question is answered, not '(solved)' in the title."
Or something more general, "Only marking a response as correct is needed to inform viewers that your question has been solved."
And the sidebar here is hopefully to find a way to improve our SO google results to show the searcher that the question they're looking at has an accepted answer, versus one that does not!
Screenshot to clarify:
[solved]
to a title mean that more people might do it (bad)? SO as a whole is generally very quick at editing out the new ones, as you've noted, though some of the older ones may still be hanging around.