These are one of the same markers I use to mark the edges of the tools I need to sharpen. A small investment buying a marker saves on tool steel long term. By marking the edge and then testing it against a grinder stone you can eliminate errors in setup and lengthen the life of your tools.  Also great for anyone who needs a black marker!
 
Pentel Black N50 is a robust everyday permanent marker. This Robust permanent marker will write on almost any surface including metal, wood, glass, card and plastic. It has a metal barrel, perfect for long lasting in more harsh working environments! No wonder they're the number one choice for industry and commerce. The ink is fast drying yet rich in colour. Ink flow is controlled by a valve mechanism to allow a precise application.