Did the whole shebang happen under the radar?
If that ring on that finger is what it seems to be, it could mean Theroux and Jennifer Aniston already tied the knot without anyone knowing about it. And although that's not unheard of in Hollywood, it would still be a huge bummer (but also very impressive seeing how it's only been a week).
Aniston was recently spotted, but her rock has yet to be revealed since she was in character for her next project.
Maybe Justin is just letting ladies know he's off the market by sporting some bling on his finger—yeah, that's gotta be it.