I hope this is the proper forum...
I had purchased a used SW 5906 in Stainless Steel and a Beretta 96 INOX some weeks ago. The sights on both were very faded and not much use. At first I tried using a white crayon as someone had suggested, but the results were poor. Next was a bunch of trials of different paints including standard enamels and acrylics. They were better, but still not quite what I'd hoped. After some more trials, I finally settled on some Rustoleum Specialty Glow In The Dark latex and some red nail polish. Both worked well.
The pictures don't really do it justice, but the Rustoleum looks quite good. I don't expect to have night sights, just something a little brighter than the standard paints.