The disclosure relates generally to geographic-based signal detection. One claims recites a method including: receiving information indicating a geographical area; with reference to at least a portion of the information indicating a geographical area, selecting a machine-readable indicia detector that corresponds to the information indicating a geographical area; using a programmed processor, processing machine-readable indicia with the selected machine-readable indicia detector to obtain a plural-bit message; and carrying out an action using the plural-bit message. Of course, other claims and combinations are provided as well.