A method of enabling user interaction with computer software running in a computer system via an interface surface and a sensing device. The interface surface contains information relating to the computer software and coded data indicative of a signature field relating to the computer software. When the sensing device is placed in an operative position relative to the interface surface, it senses indicating data indicative of the signature field. The sensing device also generates movement data indicative of the sensing device's movement. The indicating data and the movement data are received from the sensing device, and the signature field is identified. Once the signature has been identified, the computer software is operated in reliance on the movement data, and in accordance with instructions associated with the signature field.