This disclosure relates to advanced image signal processing technology including encoded signals and digital watermarking. One claim is directed to a container comprising: a 3004 or 3003 aluminum alloy shell, the shell comprising an outer surface and an inner surface; a first layer of transparent ink printed on the outer surface as a flood within a first region; a second layer of the transparent ink printed over the first layer of transparent ink within the first region, in which the second layer of the transparent ink is printed to include a plurality of holes without any transparent ink printed therein; an opaque ink printed within the plurality of holes of the second layer of transparent ink on first layer of transparent ink within the first region, in which: i) the outer surface/first layer/second layer, and ii) the outer surface/first layer/opaque ink comprise a spectral reflectance difference at a machine-vision wavelength in the range of 8%-35%, and in which the plurality of holes are arranged in a 2-dimensional pattern according to a machine-readable signal, the 2-dimensional pattern being machine-readable from imagery captured of the first region. Of course, other containers, methods, packages, objects, systems, technology and apparatus are described in this disclosure.