I have a 6 stall roundhouse. What system do you all use to know which engine, is in which stall; to acquire a loco? The house is too far to actually see into to read the numbers. I have decals on the fixed open doors and inbound tracts for operators to choose.
In side of roundhouses was a big blackboard. on this blackboard was a line for each track. On this line was written information on needed repairs that needed to be made. So you do the same thing. If you only have 6 locomotive you just assign to a track and that is it.
This is also the reason a lot of roads put the loco numbers on the backs of the tenders. Anyone out in the turntable area knew exactly which loco was where.
I just lift the roof... ;D
Ton
On the edge of the layout, you could make a little turntable and stall diagram in white paint on a black background. Use blackboard paint for the black, and then you can just chalk the engine number or decoder channel for the units in each stall.