Now, you really can't make out the cab markings on 4012 to well in this picture, but, if you squint hard enough and have a big enough monitor, you'd see this:
This is what they mean:
UP= Union Pacific Railroad
4002= Number of the Locomotive
4-8-8-4= Wheel Arrangement of a BigBoy
68= Size of Drivers
23 3/4 - 23 3/4= Diameter of the front and rear cylinders
32= Piston Stroke
540= Total weight on drivers: 540,000lbs
MB= Stoker Type
The reasoning behind these cab markings is to allow engine hostlers in the yards to quickly see what type of engine they are working with and it's statistics. An engine hostler is an engineer who's job is to move engines around the yards, fuel them and bring them to and from the roundhouse.
