The present disclosure relates to signal processing such as image processing, signal encoding, digital watermarking and data hiding. A sparse or dense digital watermark signal can be conveyed with a narrow-band absorption material corresponding to a center wavelength of a Point of Sale (POS) barcode scanner. The POS barcode scanner typically captures 2D imagery. Since the narrow-band absorption material absorbs over a narrow-band it is relatively imperceptible to the Human Visual System (HVS) but can be seen by the POS scanner.