An electronic system which facilitates active signs for car park management systems. One such method computes a content specific message dependent on the host signal, encodes the content specific message into a watermark signal, and embeds the watermark in the host signal such that the watermark signal is substantially imperceptible in the host signal. value than that of the products in the conventional methods. Authorization to access patient health information stored on the implantable medical device is authenticated using an ambulatory repeater. The testing assembly is characterized by a coating being applied to the outer surface of the roller to define a contact surface of the roller.