Materials:

Self Hardening Clay (Can also use Fimo or Sculpy clay which can be dried in the 
oven quicker.)
Inscribing Instrument

Form a small amount of clay into a ball.
Flatten into a thin disk approximately 1/8 inch in thickness (Can also be 
square, or any shape you feel comfortable with.)
Inscribe your rune designs into clay.
Allow to air dry (Or cool, if baked in oven.)
Store in a pouch or box until ready to be used.

Links to find Pics of Runes