Google has a complex policy regarding the use of ad targeting based on trademarked names. In many countries -- Australia, Brazil, China, Hong Kong, Macau, New Zealand, North Korea, South Korea, or Taiwan -- Pepsi cannot buy AdWords triggered by people searching for "Coke" if the intention is to get people to click on a site for Pepsi. And you cannot use the word "Coke" in your ad if you are Pepsi.