I mark the change of seasons in two ways:
1. Every fall, after several days of cool weather, I order my first hot coffee of the season. Once the switch has been made, there's no going back to iced until springtime, not even if it gets warm for a day or two in late October. I switched to hot coffee this past Saturday, after that long run in the pouring rain.
2. Since I have limited drawer space, clothing that isn't currently used gets packed away and put into storage. Tonight, I packed away the summer tank tops and skirts and pulled out the sweaters and corduroy. As a tribute, I made a Stortrooper of myself (inspired by Maria and Brigita) dressed in fall clothes.