Digital BW, The Print

Pencil lasts a very long time! If you find that you want to use a pen 
(or brush) and ink, I suggest using the same ink that you used to 
print the image. If you use third party inks, most likely you have a 
bottle within reach. If you use OEM cartidges, there should be enough 
left in the "empty" cart for a very large number of signatures, etc. 
DuPont has a white solvent inkjet ink if you need to sign/number over 
a dark area.