Following on from hereward's post, I found this photo of a loco with light above and associated signage :
http://www.railroadforums.com/photos...8/limit/recent
Typically, a yard crew will be despatched with a work list detailing which blocks of cars are to be moved from a consist on a specified track and moved to another (this is pullback switching). In larger yards there will be multiple tracks, storing different consists, the tracks coming together at each end (the high and the low end) where the tracks leave the yard.
All switching is done manually by the yard crew, the engineer being just part of the team. The benefit being that the engineer can see the switching operation better and can move independently in the yard as the locomotive picks up and drops off blocks between tracks. The other members are coupling/uncoupling cars and setting the switches.
The crew will often ride the block of cars although they are not supposed to.
My apologies for using North American terminology, I trust you can understand the terms.