Using a chrome paint pen would probably be the easiest way to do it, iirc ZEYAR is a pretty good brand that a few other customizers here use
A harder-wearing option that wouldn't smudge as soon as you touched it or looked at it funny would be using a gloss black base then airbrushing a chrome paint such as Hyperchrome by SMS or Alclad II chrome. Spraying a gloss black base and rubbing some chrome nail powder in while it's a little tacky would work as well, though that leaves a somewhat sparkly look at times from my experience.
