It’s the Little Details
Since James Cameron was trying to connect audiences to the story, there are a few hidden Easter eggs throughout the film. There are a lot of little details that really happened, which made the movie even more magical. In the last heart-breaking scene of the movie, you see Rose coming down the grand staircase where she seems to be touching a memory, or even a dream of present-day-rose.
Source: Tumblr
You probably remember how in that scene, Jack holds his hand out to grab Rose’s. What you may have not realized is that there is a clock behind him, and it reads 2:20am. That happens to be the exact same time that the Titanic sank into the ocean. This was obviously done intentionally, but most people don’t notice such a minor detail.