Google’s Adsense explains themed ad units as such:
What are themed ad units?
As part of our ongoing effort to provide ad designs that will improve results for both advertisers and publishers, we now offer themed ad units – ad units that display themed colors and graphics during holidays and special events. You can view examples of themed ad units by visiting our Ad Formats page.
Whenever themed ad units are available, we’ll display them only to users in the appropriate locations, as determined by user IP address. For example, Fourth of July-themed ads would be visible only to users located in the U.S., while users throughout the world might see ads with a New Year’s Eve theme.
You can enable or disable themed ad units by following these steps:
- Log in to your account at www.google.com/adsense.
- Go to the My Account tab.
- On the Account Settings page, scroll down to the ‘Ad Type Preferences’ section and click ‘Edit.’
- Depending on your preference, check or uncheck the box next to ‘Enable themed ad units when available.’
- Click ‘Save changes.’ Your selection will apply to all your AdSense ad units.
yada yada yada bla bla bla.. what I really wanna know is, How Do I Get My Theme Ads?! Along with some other questions: