like these two parts for example:
(1) "My powers stretch across the globe" == a traffic light's "powers" stretch maybe 100 feet.....they may be located all over the world, but the power of a traffic light is only as far away as one can see it.
(2) "But idle they all stand." ==== idle, as in not moving or changing?? um, i think traffic lights change color all the time. and if the answer to your riddle is trafic lights, then this statement which you said refers to signs does not apply.