I found these at Savers the other night after I dropped the Tot off for football practice. They're decals from Duro Decal Co., Inc. Apparently, they are still in business, although they don't maintain a presence on the world wide web. I found out a lot about them here.
According to the directions on the back of the decals I just cut out the design, put it in a dish of warm water for 30-45 seconds, then slide the design off the paper and onto whatever surface I want to decorate. After that, I press and smooth out all the air bubbles and let it dry.