The Departed : The whole "X" thing (Spoilers)

So I was aware going into the film (somewhat unfortunately) that "X" shapes in a scene symbolise the eventual death of the character on-screen.

There's one scene in particular that I'm curious about. Forgive my lack of using the in-film names of the characters. When Dicaprio's character meets with Matt Damon's girlfriend at her home before they fuck (making them both less likable characters than the one Matt Damon plays, imo), there's some window shots that show the "X" over the female character. So when she later locks herself in a room after an argument with Matt Damon, I honestly thought she had killed herself until she turns up again fairly soon.

Were the "X" shapes used in that scene only because Dicaprio was also in that scene? Though, I swear when it cut to the window shot, it was only her character in-frame.

Maybe she kills herself after the events we see in the film?

I had never heard this before. Apparently the usage of the X was an homage to Scarface from 1932. The X in the Dicaprio scene you mention was probably for him. This video makes it look like they used the X on him multiple times.

Yeah, Dicaprio and Damon's character have numerous scenes with at least one "X". If you've seen the movie unaware of the visual hints, it's definitely a fun novelty trying to spot them all the next time. I think the movie isn't as genius as some people make it out to be, but it's still a fun experience.