Do I need to say much more?
When Wyatt and I visited Travel Town in Los Angeles (just off Zoo Drive), I took my camera along and to my amused surprise, I found stenciled on the back of one of the train cars the phrase "Do Not Hump"
Okay... so I don't get a flood of emails...
Do Not Hump is a train phrase that directs the train yard workers what Not to do to the train car. With common freight cars, the use of a man-made hill is used in the sorting of freight cars; this is called "humping." A single track on a hill has a number of branches on the downhill side resulting in a number of parallel tracks. So a worker (usually in a switching tower) knowing a car's destination and using gravity (along with a nudge) throws levers/switches to direct which line the car will ride on. This allows them to sort the cars and "build" the train. However, while humping is a quick method to sort train cars, it can be a rough ride, as the car is at the mercy of gravity. There are "retarders," which are supposed to slow things down and prevent cars from crashing into each other (potentially damaging multiple cars), sometimes the cars derail (which is not a good thing) and in most cases the ride is just rough causing damage to the content of the train car. So those cars that need "special handling" (such as certain passenger cars, hazardous material cars, etc.) have stenciled on them "Do Not Hump." When a worker comes across a car with "Do Not Hump" on it, they move it aside for special handling and do not allow it to roll down the hump unattended; uncontrolled.