You could decorate with gourds, pine cones, acorns, and a red or orange candle. To them it would look like a fall decoration, but you would be using symbols and colors of Mabon. Take a walk in the woods or a park, or even just around the yard and notice the changes the cooler weather brings. Silently give thanks to your higher power for the summer which is ending and the autumn that's approaching. Check out the Holidays section on this website, it has a good bit of information. Your Mabon celebration doesn't have to be big and flashy, it just has to have meaning for you.