I don't know if its still there, but back in the woods near Lake Roland in Baltimore is a steel plate bridge on the old Greenspring Valley line that had Penn Central spelled out on it with a White P Red C worm on it. The line has been abandoned for years, and getting to it requires quite a hike along the old roadbed from Robert E. Lee Park off of Falls Road. This bridge is in the middle of nowhere, and I can only imagine that the crew painted the stencils on to practice for the bridges people would actually see. If memory serves, the stencils are only on one side of the bridge, too.
It's been a few years, and I no longer live in the area, so it would be hard to verify if it is still intact. If someone in the B'more area is feeling ambitious, this is a nice time of year to hike back into the woods. Check out your Geological Survey maps, or an old PC system map, and you'll see where the bridge is.
You may want to think twice, though, if you saw Blair Witch recently.