The present invention provides steganographic-embedding techniques. In one implementation a digital watermark signal is mapped to a set of spatial positions. Physical message objects are positioned according to the set of spatial positions. The signal is provided on a physical structure such as a building or road. The signal may include geo-location information. The geo-location information identifies the location of the physical structure. In other cases the signal includes a marker or identifier. The marker or identifier provides a reference point for images depicting the physical structure.