Let's face it. Once or twice (or more), you've ridden the 'el' and wanted one of these. But the train's always too full or you're in a hurry... or you're just scared. Not that I blame you. I, like you, have always wanted one of these wonderfully grimy signs depicting Chicago's most valuable form of transportation. And I too have been way too nervous (and way too short) to manage to confiscate one properly.
A few months ago though, I was riding the train towards the loop and sat beside a group of students from Loyola. I incidentally befriended a rather drunk young man from Loyola whom we shall call Cliff for the purpose of anonymity. Anyway, I ended up expressing my interest in confiscating a sign, and the next thing I knew he was standing on top of the seat, and pulling down the infamous plastic sign. It ripped in half. But Cliff was relentless, and somehow managed to steal the sign on the door across from it. So now you know. It's possible. Just make sure you're in a car where nobody cares... and be careful not to rip it in half! :)