You just need a few drops of blood. Pierce your index finger with a needle, either sterilized (with rubbing alcohol) sewing needle or a diabetic lancet. Then take the pen and dab it in the blood, and then sign your name. When I sign my name in blood for something, I also dab the remaining blood from my fingertip onto my signature. But thats just me.
For my pledge of dedication, it says I must write my name in blood. Does this mean just my first name? First and last? First, middle initial, and last? Or my full name?