Only 25 percent of all PC users fully utilize their computer’s energy saving features. The LBL hypothesizes that these high levels of disabling are caused, in part, by the varied and confusing office equipment power control interfaces. The LBL proposes that by making power management controls more intuitive and consistent across all office equipment, people will enable energy saving features more fully and thereby reduce overall energy consumption. An international standard for the symbols does exist (IEC 60417 and ISO 7000); however, those few manufacturers that adhere to the standard often implement it in different ways.
(via this old discussion about orange XML buttons