Edit 2013-05-26 With the new version if Google Maps a Google+ account is probably not needed.
Edit tl;dr You can star locations once you've checked in to them from Google+.
Here's a way I managed using my iPad and Google Maps in Safari. You have to have a Google+ account.
- Write a status statement (like a "check in") from Google+ making sure you've specified the the location (i.e., the train station) when you enter the status. If Google+ can't find the location by default, you'll have to type it into the "Search for a nearby location" box.
- Go to Google Maps in the Safari browser and make sure you're logged in to the same Google account you used for Google+ in step 1. Go to the "My Places" menu to show the list of your places. The train station you "checked in" from will show up in the list. You can now click the star icon of this location, and it'll show up in your map in Google Maps (Safari).
The following shows a bus stop called "Peel / Notre-Dame" in Montreal where I did a check-in using Google+, and it can now be starred in Maps under "My Places":
I know the Android version of Google Maps app is much more powerful than the iOS version (this won't work on iPad's Google Maps App - it has to be the Safari version). But the Google+ check-in seems to be the key to get the place to be "starable".