Driving safety indicator (DSI + WSI) The percentage figures on the centre of the tire simply indicate how much of the tread remains in the main grooves of the tire. The numbers fade away as the tire wears down. Similarly, the snowflake symbol is a winter safety indicator. It remains visible as long as there is at least 40% of groove depth left. Once the snowflake symbol wears off, the driver should buy new winter tires to ensure adequate safety.