You'll notice when you open your map (by hitting M or the little magnifying glass under the mini map) that there is a new subway icon in the top bar.
When you hit it you'll see the 2 subway lines, and if you're in one of the stations it will tell you which stop is next!
Buy your next Red or Blue ticket in confidence knowing where you will go!
Feedback is appreciated :D
Note: if you are currently playing, you might have to reload the game in order to see this.