Abstract: A system is provided for preventing the contamination of milk. First, a milk contaminating condition is identified in dairy cattle or other milk producing animals. The condition typically results from the animal being treated with an antibiotic. A manually attachable contamination indicating marker is provided for the animal. The marker is secured in the vicinity of the animal's udder and is positioned so that milking cannot be conducted without the hands coming into close proximity to the marker. The marker is maintained on the animal until the milk again becomes wholesome viz. to the end of the withdrawal period for the particular antibiotic that is being used or other period required for decontamination of the milk. The marker has a label bearing surface with a written message that serves as a reminder to segregate or discard the milk and a fastener for securing the marker to the animal in close proximity to the udder and preferably immediately laterally thereof.