Abstract: A characteristic feature on a generally longitudinal member is detected as the member is longitudinally advanced on a path extending from a first position to a second position. Based on the detection of the feature on the member and monitoring of the advance of the member on the path, indicia can be applied to a desired position on the member. The detected feature can be an S-Z reversal existing or created on a strand of S-Z stranded optical fiber buffer tubes included in an optical fiber cable which is undergoing cable manufacture along a cabling line. Intensity data values representative of an optical image sample of the strand with the S-Z reversal feature, where the image sample is obtained by an optical radiation detector coupled to the path, are processed for identifying the S-Z reversal feature on the strand.