The idea of "antiquing" a finish on ceramics comes to mind. Perhaps a search on that may help.
This is also a common concern for people on classic automotive sites, though they are usually filling in larger areas on emblems - but it might help and give a few ideas, at least for a paint that is durable.
Similar to antiquing, my grandfather had filled marks on some tools (scales and micrometers) by applying an ink or other substance, and rubbing it off. It stayed in the engraved areas quite well. Unfortunately, I don't know how this may affect the finish on your camera, as the cosmetics are more important than simply being able to read the markings on a machinists scale.