A Navigator’s warrant seal is molded from bone, though what the bone came from is generally only known to the person who made it. Could be human, could be demon, or an animal.
The seals are authenticated by dipping them in blood and rolling them out on a special sheet of paper. If the seal is properly consecrated and warded, the blood will hold, otherwise it begins to noticeably boil off after a few seconds.

Vasha Fairzant’s skeletal arm is made up of bones taken from a human arm, though not her missing one; that arm belongs to someone else now.