So I decided to try my hand at a quick touchmark. I wasn't sure if anyone was using an N which I'm sure is being or has been so I did a backwards one just to see how hard it would be to file in and if it would work. 

I have been thinking of making one myself. Nice work Nick. 

Try to get the letter cut with a square edge rather than sloped as you've got it.  It takes less force to get them to leave a stronger impression.

It doesn't take much depth either so you don't need to remove much from what you've got.  A small chisel would likely do the trick.

Thanks Das, gotta keep me posted if you try one.

rockstar, thanks for the tip, it worked better than I thought but I will try cutting the edges a bit with a chisel a bit.