Though initially this move might seem like a minor footnote, it’s actually a pretty big deal. It positions Facebook in direct opposition to Twitter, whose IPO is largely predicated on TV and advertising dominance. Facebook’s feature works like this: Users who like a show’s Facebook Page can choose an option to get reminders about when that show starts. It’s a simple premise, but it plays into two important trends: social’s integration into TV via the second screen, and notifications as subtle forms of advertising. How well the move pays off for Facebook could be a big indication of the effectiveness of both trends.