Many websites, such as news sites and blogs, join the Google Display Network, which enables Google to show ads on their sites. It's our goal to make these ads as relevant as possible for you. While we often show you ads based on the content of the page you are viewing, we also show some ads that you might find useful based on the types of websites you like to visit.
http://support.google.com/ads/bin/answer.py?hl=en&answer=2662749
DU doesn't have "Adult" ads (not that I've seen) but it does have "Non Family" ads, which makes sense because it isn't a "Family" site.
Google's definition of "Non Family" is:
adult-oriented content without nudity or sexually explicit content... might include adult language, concepts, or images that aren't appropriate for all audiences.
http://support.google.com/adwords/bin/answer.py?hl=en&answer=116446&topic=24937
"Non Family" seems the most appropriate setting for DU because many political ads and discussions are "non-family."