Sometimes when Siobhan watches a movie I don't know, I'll try to identify, within a couple of minutes of it being on, what year it was made in. Obviously some movies make this so obvious it's not a challenge, but most don't. Identifying the year depends on a lot of factors. Mostly I go by stylistic things like the filming quality, the background music, fonts used in credits, cinematography aspects like camera angles and use of split screen, and more obvious things like who is appearing in the movie and the way they talk. Usually I'll try to do it without knowing the title of the movie, too.
Perhaps surprisingly, on movies after, say, 1960, I can usually hit within a couple of years, even only with a couple of minutes of screen time. I'm not even always sure how I can peg a movie's year, but I almost always can. And I'm almost never off by more than 3-4 years.
The trick to this game is if you're a big movie buff, so logically you should be good at it, you also can't really play it because odds are you'd already know too many of the movies directly. I'm not a big movie buff; outside of the few genres I like, there are tons of movies, even some of those big classics everyone has seen. (Heck, I don't think I've ever seen Casablanca from one end to the other all at once, though I'm sure I've seen all of it piecemeal.) So even if you take people who have enough movie experience to play but not so much to be excluded, like me, I wonder what makes one person better at it than the other?