To mark a particular location, press the "MRK" button. The display will read: "Mark?" Press the "MRK" button again to assign a label to it. There are four (4) labels: Red Light, Speed Camera, Speed Trap and Other. To scroll through the labels, simply press the volume (+) or (-) buttons until you reach the desired label. Once you've selected the label, press the "MRK" button again to confirm.