those markings might be from some sort of visual inspection (quality asurance)
3rd pic from the bottom, is that rod part of the infamous wastegate apparatus ??
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I just noticed in the 3rd from the last picture, the wastegate actuator rod has some paint marks by the circlip. I wonder if this is some kind of a anti-tamper marking?
Those sort of markings allow easy identification to ensure nuts/bolts/clips haven't loosened off. Indirectly they allow tampering to be observed, but that isn't their original or real purpose. Heavily used in motorsport where things become quickly loose.