We present an authenticate graphical barcode symbology, and describe a system for its reliable encoding and decoding is presented. The graphical barcode is generated by modulating halftone patterns according to the message to be embedded in the barcode during the rendering of a base image. The generated barcode has the appearance of the base image, and when it is printed and scanned back in, the message can be retrieved. A graphical indicium is a graphical barcode embedded with a digitally signed message such that the integrity and authenticity of the message can be verified.