A digitized signal is published with a blank watermark, i.e., a watermark which contains no specific watermark data, and a server computer system encodes specific watermark data into the watermark signal for each delivery of the digitized signal. A basis signal which is used to watermark a digitized signal is predetermined to enable embedding of transaction-specific watermark data to be embedded in the subject signal with minimal processing resources. Since the basis signal generally accounts for the majority of the processing resources required to watermark the subject signal, only a relatively small portion of the requisite processing resources are used to embed transaction-specific watermark into the subject signal.