A method of limiting communication between an application and a user, via a sensing device interacting with machine-readable coded data printed on a surface, the method comprising the steps, performed in a computer system, of: receiving interaction data representing the interaction of the sensing device with the coded data, the interaction data enabling identification of the application; transmitting information based on at least some of the interaction data to the application; and enabling transmission of up to a predetermined number of electronic messages from the application to the user.