One of the reasons I've been hesitant to buy out of home advertising on commuter trains over the years is that the ads simply get messed with all the time. If you've ever seen a Long Island Rail Road train with a broken door, sometimes you'll see that someone has performed a monkey-rig fix by using a piece of one of the ads to tape the doors shut so that they'll stay closed. Woe is you if you happen to represent the advertiser who paid for the ad.
But sometimes, the ads are defaced in interesting ways. Here's a really blurry (my camera phone sucks) photo of a State Farm ad featuring a baby. As you can see, someone cut out a bottle of liquor from another ad on the train and stuck it on the State Farm ad, so it looks like the baby is chugging right from the bottle. Funny, yes. Confidence-instilling for advertisers, no.