A self contained writing pad unit (1) comprises a pressure pad (7) for sensing movement of a writing instrument over a contact surface (2) of the unit when a user writes a sign, for example a signature, either directly on the contact surface or on a writing medium (4) supported by the contact surface....http://www.google.de/patents/US4752965?utm_source=gb-gplus-sharePatent US4752965 - Sign verification
