Thanks all for the suggestions!
I found acrylic paint (water based) works the best, although a bit pain in the butt to apply.
I use q-tips to fill pain in the the engravings, let it dry for few minutes, then wipe with very slightly damp cloth. Trick is in timing for paint to dry and amount of moisture on the cloth. It's a delicate balance. If cloth is too wet it will remove some paint from the engravings, then you have to repeat process 2-3 times. Each time more and more paint stays in the etching.
Also I use 2 cloth pieces. One for wiping out paint, and second one for cleaning up residue left over from wet cloth (it's easy to cleanup).
I use this process in filling up text on my Xronos clocks
Of course best way would be to use silk screen printing, but kit is somewhat expensive...
And DO NOT use nail polisher! It will not remove at all, I think it eats in the acrylic