To a novice, the easiest way to identify a winter tyre is to look for a symbol of three-peak mountain and snowflake (3PMSF) on the tyre wall as well as the letters M and S (mud and snow). The 3PSMF symbol indicates that the tyre has passed a minimum required performance on snow as laid out in EU Regulation 661/2009 on the Safety of Motor Vehicles.
This is a relatively new regulation, brought in in November 2012. The M + S symbol has been used by tyre manufacturers for years to differentiate their winter tyres from their summer ones.
Winter tyre treads are deeper which allows snow and slush to build up in the cavities. Strangely, snow is excellent for gripping onto snow so these deep treads really help with traction. For this reason, it’s important to replace winter tyres before the tread reaches its legal minimum of 1.6mm.