The snowflake mountain symbol isn't a good overall guarantee about winter performance (only means the tires pass an acceleration test on medium packed snow). Dedicated snow tires (Blizzaks, Michelin X-Ice, Nokian, etc) also have the snowflake mountain symbol but also have enhanced braking, handling, ice traction, etc based on their softer rubber compounds, siping, tread pattern, etc. Unfortunately, these enhanced winter driving characteristics come at the expense of tread wear.
From Tire Rack's website:
A three-peak mountain snowflake (3PMSF) symbol branded on a tire's sidewall indicates the tire meets required performance criteria in snow testing to be considered severe snow service-rated. Originally used as a designation for winter tires, the 3PMSF symbol is now featured on some all-season and all-terrain tires with snow performance that meets the testing criteria.
- Testing measures a tire's acceleration traction on medium-packed snow only. Braking and turning on snow, along with ice traction are not components of the test.
- Tires branded with the 3PMSF symbol are expected to provide improved snow traction beyond a standard M+S branded all-season tire.
Note: 3PMSF-branded all-season and all-terrain tires cannot match the traction of dedicated winter / snow tires in all winter weather conditions and should not be considered a replacement for where and when a dedicated winter tire is needed.
