Question: Why would you oil a Stormtrooper?
Answer: Because it says so!
At the age of four, I was convinced that the markings on the back of your garden variety Stormtrooper spelled out the word “Oil.” As a result, I spent the later part of the 70's believing that these white-clad warriors were actually robots. In fact, I vividly recall debating the issue with my older cousin Jamie while munching down Happy Meals in the fall of 1979.
“Don't be an idiot!” Jamie scoffed with a mouthful of fries, “If they were robots, how could Han and Luke wear their armor to sneak around the Death Star?!”
“Obviously, by skinning the robots of their armor-plating,” I sneered, followed with a perfectly timed belch.
But what do these symbols really mean?
According to the original designer, Andrew Ainsworth, they were just shapes used to fill the empty space across the back. The circle was created with a plastic part they had lying around the workshop, possibly a lid to a container, while the two vertical lines were just bits of wood they added to the mould.
Damn you, reality! That's not nearly as exciting as a giant, sculpted sign spelling out where to lubricate these ivory commandos!!