In London, you will rarely see an empty car, if you do, its still safe to go in. If you see one in NYC, that means it smells awful and everyone has avoided it!

Some of the platforms ave installed information on time to upcoming trains, which is a great help.

Once you establish local and express trains (and which stations they go to), the NYC makes much more sense. The caveat is Express trains can still run local and it can be hard to decipher on the wretched PA system.

For London (and many subway systems), you need to know what the terminal stop is to know which train to enter. Not so difficult as maps are at each entrance of the platform.