Credit:
It's a new campaign devised to protect users from getting scammed; Microsoft worked with the US Federal Trade Commission (FTC), Postal Inspection Service, and Western Union to provide public service announcements (PSAs) in the form of ads on Bing results pages.
The ads should appear for relevant keywords only; I've tried about a dozen different combinations, and haven't seen them, but it could be because I'm not located in the USA. You should see them if you're looking for foreclosure rescue, lottery, and fixing credit problems. If you click on one, you'll land on trade commission or Microsoft Web pages containing advice about avoiding online scams.