Look at the process - the forging and machining processes for the individual parts used oil to reduce friction, it's a common process technique. The individual components are sub-assembled and I doubt they were cleaned to remove the oil (maybe drip dry), plus any remaining oil was also a rust inhibitor. Somewhere, after receiving or pre/post quality inspection, the paint dab was applied for identification. It was applied to an oily surface. The dab was useful for assembly line purposes, so if it came off around the time the finished car was loaded on a truck or train, nobody cared. The paint dab would not be on a service assembly.
As Bob Gaines said, leave it off.
Jim