Demon's signatures are designed to disguise their actual names. They are usually signed in blood. If there is a mass of signatures, they are usually signed in a circle, a doctrine of signatures..
There are a number of alleged demon signatures in existence, some or all perhaps faked.
Some books on demonology, like Arbatel de Magia Verum and The Lesser Key of Solomon (or Lemegeton), assert that all demons have their own signature, collectively called seal of the demons, and sign the acts of diabolical pacts with them.
These 'seals' (not seals in the usual sense, as they are handwritten) are imaginative lineal drawings, often complicated. It is notable that many of these signatures include the sign of the cross, which according to Christian tradition is opposed to demons and scares them. These signs appeared mostly during the Renaissance, in a time in which demonology was a subject of study for many theologians, priests, alchemists, cabalists and other scientists and pseudo-scientists. One of the accusations by which the Inquisition sentenced Urbain Grandier to death was based on several of these signatures.