The urban myth that I grew up with was that they were pointing at a hidden camera to show the dispatcher that they're awake, but the article I linked below suggests that it was taken directly from the Japanese railway.
[1]: https://www.nydailynews.com/new-york/mta-conductors-point-st...
> ... New York City’s MTA subway system, whose conductors have used a modified point-only system since 1996 after then Chief Transportation Officer Nathaniel Ford was fascinated by the point-and-call system during a business trip to Japan. In the MTA’s case, conductors point to a fixed black-and-white “zebra board” to confirm a stopped train is correctly located along the platform.
> According to MTA spokeswoman Amanda Kwan, conductors were quick to adapt to the new system, and within two years of implementation, incidents of incorrectly berthed subways fell 57 percent.
https://imgs.6sqft.com/wp-content/uploads/2016/05/12133255/N...
So if you want, you can meet someone on a specific train car if you stand somewhere in relation to the board.
I used to meet up with my wife who worked 2 stations north of me using this technique without either of us disembarking. It was pretty handy.
1. Does the NYC subway as a result have significantly lower incidence of alignment problems than London's Underground? London has had one person operation of all trains across the system for decades, so, if the conductor pointing at stuff matters, logically not having a conductor at all ought to result in significantly more errors... I haven't heard of such errors at all, but presumably they do happen at least sometimes.
2. What do the rates look like in Copenhagen, which is GoA4 and thus there isn't anybody aboard the train with responsibility for the system, there's a control centre with some broad over-all authority, but individual trains drive themselves.
My instinct is that actually this is not a good solution, it's what you might do if all the good solutions are off the table and you have to pay these guys anyway. "Well, might as well try to slightly improve our lousy accuracy".
However not all underground platforms on each line are of uniform length - for example Baker Street's subsurface lines have platforms shorter than the trains that run on them.