The present invention relates generally to steganographic encoding. Once claim recites a method including: obtaining plural-bit auxiliary data; creating an original carrier signal representing the plural-bit auxiliary data; reducing information content of the original carrier signal so that the carrier still conveys the plural-bit auxiliary data, yielding a reduced carrier signal; and hiding the reduced carrier signal in host data. Another claim recites a mechanical part including: a metallic surface including a pattern, the pattern conveying plural-bit auxiliary data in a steganographic manner, and the pattern provides at least diffuse reflection. Of course, other claims and combinations are also provided.