A great little short story at Folklore.org explains the origins of the Command key symbol.
“There are too many Apples on the screen! It’s ridiculous! We’re taking the Apple logo in vain! We’ve got to stop doing that!”
After we told him that we had to display the command key symbol with each item that had one, he told us that we better find a different symbol to use instead of the Apple logo, and, because it affected both the manuals and the keyboard hardware, we only had a few days to come up with something else.