I saw this out in San Francisco a few years ago - when you got on a train they handed out tags to put on your bike to indicate where you were getting off. 

Here, I made up on own tag on a 3x5 card.  On the other side of the same car I put Jefferson Park, for the return trip.  I only do this once a month, and not every cyclists recognizes this.  But it might help playing "Musical Bikes" on Metra when it's crowded.