Draht

vurm blood is used to create drahts - glowing, unique identity symbols for the ultra-conservative Dwarfs known as Deep-Downers - which are made by tattooing vurm blood under the skin. This is a powerful concept in Dwarf society. when Samuel Vimes gets something similar on his skin, but from a different source, Dwarfs respond with awe and respect. Which Sam knows exactly how to exploit.