Several people have raised the question about how to determine which marker lamps or flags go where and when on a locomotive. One of the best sources for information on such subjects are the various railroad rulebooks. Allen Cain took the time to scan the Southern Railway Rulebook effective April, 1943. Here are the pages of the that rulebook on signals placement, type, and color for locomotives. Click on the thumbnail for a full size image (each 800x600 but >100kb).
Thanks to Allen. If anyone else would like to add more information (particularly for other southeastern railroads), please contact the webmaster!