The snowflake in the mountain symbol is not a marketing tool, except to the extent that if the symbol is on the tire, that tells you that the tire meets the tire manufacturers' self-imposed criteria for the symbol. These criteria are based on the actual traction of the tire. The symbol and the criteria for it were adopted because the criteria for tires to have the MS, M/S, or M+S rating (all of which mean mud and snow are the same thing) is based solely on the type of tread. For the M+S rating the tread must meet certain criteria based on the size of the tread blocks (which must be large) and the gaps between the blocks. This does not necessarily, or always, translate to superior traction on ice and hardpacked snow or deep snow. Tests have shown that M+S rated AT tires do not have as much traction as a true winter tire with the snowflake inside the mountain symbol.
In addition, one reason that winter (or snow) tires have superior traction is that a true winter tire is made of a softer compound than other types of tires, including the AT tires with the M+S symbol. The softer compound gives the tire a better grip on ice and hardpacked snow in cold weather. Most tires with the snowflake in the mountain rating are made of a softer compound. Many, if not most, tires with the M+S symbol are not.
And remember, the more sipes, the better the traction on ice and hardpacked snow, on both true winter tires and M+S rated AT's. Add studs to the true winter tire and the traction difference between those tires and M+S rated AT's is very high. I know, I've run numerous brands and models of both types of tire in the winter.