Abstract: 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. Electronics (8) including a RAM and timing systems determine data relating to the original signature. A power supply (9) is provided to enable operation of the electronics (8). The unit (1) is portable and the data represents dynamic characteristic features of the writing signature.