I have been using a BIC Ultra Fine Point permanent marker and apart from my unsteady hand, it seems to be working out OK: -
I polished the plate with a product called Liquid Protection metal polish made by Ferro.
It was a product given to me by my metal polisher when he did all my bright work.
It is a thin creamy liquid which works a treat

Then I set up the panel in a clamp and using my closeup specs and a magnifying glass, I was able to fill in the punched letters.
A few smudges but another careful polish should remove those.
The switch panel didn't turn out too well, the letters are poorly punched.
I might have to go over them and carefully re-punch them a bit deeper.
When I am happy with them I might give them a coat of high gloss clear for protection
