When registering the Sims 3 Seasons, players will get a Seasons Wall Decal Pack. No photo is available at the moment, but thanks to Rincon del Simmer, the source code/cache of the site gives us details of the content.
Congratulations! You have successfully registered your The Sims 3 Seasons game. Download your FREE* Seasons Wall Decal Pack now! Now your Sims can proudly liven up your blank walls and decorate with your favorite seasonal theme.