A wireless power transmitter system for directing a high energy beam towards receivers fitted with identifying signs. One type of the identifying signs may have asymmetric shape properties, such that their mirror image cannot be matched to their actual shape, even after the image is rotated, tilted or otherwise geometrically manipulated. The system can thus determine whether a detected image of a sign is a true image received directly from said receiver, or is received after the imaged beam has undergone a reflection between the receiver and the transmission system. In the latter case, the system can prevent high power transmission from being directed to a location other than a real receiver, which could be a safety hazard. Other types of identifying signs may be located in or on the borders of different zones of a transmission space, to identify zones where transmission may be allowed or prohibited.