IIRC, on the S.P. their modern locomotives had a white star painted on the center of the drivers to indicate that the locomotive was equipped with spring-pad oil lubricators on the main axles, as opposed to the heavy grease lubrication on older locomotives. The two GS-5 4-8-4s (#4458 and #4459) had several white dots at the centers of the drivers to indicate that they were equipped with roller bearings (Timkin and Symington, respectively). This was to help alert crews as to proper lubrication during hurried servicing stops.