Book of Complex Designs
A book detailing known tattoos, and providing annotated sigils for most of the library code a tattooist could need. A sizeable proportion of the book contains tattoo code so obfuscated that nobody has been able to figure out how it works; therefore tattoos with these functions are never seen without a component bearing the original author's chosen motif.
Usually only seen in hardcopy form, although parts occasionally show up scanned on some Gates.