1. A method of digital watermark processing, the method comprising: receiving a content signal; performing a watermark decoding on the content signal; from the watermark decoding, determining a watermark state of the content signal; evaluating a watermarking rule based on the watermark state to determine watermark encoding to apply to the content signal to comply with the watermarking rule; and performing the watermark encoding on the content signal to embed a digital watermark layer into the content signal; wherein the watermark rule enforces a priority of plural watermark layers by determining when to overwrite a previously embedded watermark with a new watermark layer based on the watermark state and a determined user goal; wherein the determined user goal comprises embedding watermark information to signal an event in the content signal to which a desired behavior triggered by the digital watermark layer is to be synchronized.