The letters "DWS" are visible one of the ribs on the tread area. If all three letters are visible the tire still has excellent performing capability in dry, wet and snowy weather conditions. When the tire starts to wear out the letters slowly disappear as well, first the "S" then the "W" until only the "D" remains. When only the last letter is visible, the tire no longer has good tread in wet and winter conditions, and using them then can be dangerous.