I was undecided so put no visible marks. The anodizing has lightened slightly but I would expect that where there is metal on metal interface over time.
This axle has done over 25000 miles, approx 18K of that with a SON dyno hub.
Disc brake rotational forces can be large on a hub, guessing this is causing some rotation. The Son hubs have no serrations on their inner surface which most other hubs have to provide some grip interface.
Looking at my forks (On a Tripster ATR) the fork surfaces have their own indented serrated marks probably left from originally using a serrated hub interface.
Perhaps this has happened more for you if you have used the SON hub from new.
I was considering some lightweight Allan key screw in axles as replacements for security, then a friends axle in his newish Cannondale snapped (rear hub) which put me off.