Note: Our pay per click and search engine optimization clients often ask if there is a way to stop companies from using their trademarks as pay per click or natural search keywords. Reality is that you can purchase brand names, but you can't use brand names you don't own or are not offering for sale in your ads - not because of any legality (in fact, no one is really sure about the legality of the practice - brand owners think that their trademarks suddenly disappear from the English language and everyone else thinks that you should be able to call a Ford a Ford), but because of Google and Yahoo's editorial policies.

 
Read more at: http://www.emarketer.com/Article.aspx?1004279.