I tried every marking pen out there, they work well at first for a bow or two but if you keep them a while the paint dries up and they won't mark well.
Buy yourself a bottle of archival India ink (comes in white and black) and a cheap extra fine point calligraphy pen, you will have a lifetime supply of materials to letter your bows. I like white because it stands out more as the osage darkens.
Makes nice fine lines, cover the lettering with a few coats of Tru-oil and it will be there forever.