This is all about adding snow to logo's and other other objects. Follow a number of steps that many people use as a common way of making snow (no it's not a way I've come up with, many others have before me).
Let it snow, let it snow, let it snow - well at least Sammy Cahn says so. Anyway, now that it is the season for snow, and all things cold, this is a tutorial for making snow topped objects (at the time of writing I've used this method for my winter banner).
Firstly, create the object you want to lay your snow on or open an existing image.
Now create a new layer, this will be the layer that contains the snow. Once you have done this goto the blending properties and enable "Bevel and Emboss" and "Inner Glow". Between these two effects the snow will be given a nice 3D like effect.
Now, with a decent sized brush (I prefer to use one of aroun 6px so that it's not too thick for detail) start drawing the snow where you want it.
And there you have it, snow!