When I traveled around France, one thing surprised me a bit.
I traveled all over France specifically by trains. In Paris everything was relatively simple - 20 tracks, you find yours, and the train is already standing there.
In other cities everything's a bit different. First you find your track. This is quite easy, you just need to look at the board.
However, then you come out onto a very long platform. There's letter marking on the platform. The trains arrive long and don't stay much, all are expresses. So the French came up with a system to speed up passenger boarding.
On the platform you'll find a board called "train composition". It's hard to see, but a red dot marks the place where you're standing, and you can see which letter corresponds to which car.
Or here: look how long the platform is, from A to K. Accordingly, if we're going to Rennes in car 3, we should stand between markings F and G.
By the way, interestingly, a couple times I saw trains where it wasn't clearly written where which car was. So this system not only helps to stand correctly, but also find the right car faster.