Copyright infringement is the use of works protected by copyright law without permission, infringing certain exclusive rights granted to the copyright holder, such as the right to reproduce, distribute, display or perform the protected work, or to make derivative works.
Technically it IS enough to change McDonald's to WcDonald's. I know companies are way more anal about logos used than name references in text though. Since names can't be copyrighted but logos, characters, and certain phrases can be legally trademarked and registered.
Companies are way more likely to go after someone too if they deem the work defamatory. Like a person selling shirt's with the McD's M filled with cannabis leaves is more likely to get a cease and desist than a writer with some dialogue about their characters getting McD's.
Good video on this
Biggest relevant subject touched upon in the vid, an episode of Big Bang Theory had a side-focus on the Cheesecake Factory. How did they get away with it? The beginning of the video leads up to it.