Song titles CAN be trademarked, but I think very few are, even for the most popular hits and standards.
You can trademark any word or phrase (for a specific use), but as I say, doing it with a song title is rare. You can probably name a song "she loves you" even though it would often get confused with the Beatles song of that name, but you probably couldn't get away with titling a song "let it be" because it was a huge hit song, AND it's the title of an album, AND the title of a movie about recording the album.
And you for SURE can't name a song "Theme from Star Wars" because Star Wars is a trademarked name, and there's already a "Theme from Star Wars" that the trademark holder will no doubt defend as the "true" song with that title.
This is not legal advice, IANAL, but I for sure wouldn't go up against George Lucas...