The Apple logo was a label added to the Mac command key. The official symbol for the command key is a Bowen knot[1] (‘the flower symbol’). The Apple logo label was added in later Macintosh models, meant to aide in conversion from the Apple IIe, but the label remained longer than it should’ve. The original Apple II had none of these keys. Since 2007, Apple has removed the Apple logo label from the command key in its new keyboards.
[1] http://en.wikipedia.org/wiki/Bowen_knot