the present invention provides methods and apparatus , including computer program products , implementing techniques for searching and ranking linked information sources . the techniques include receiving multiple content items from a corpus of content items ; receiving digital signatures each made by one of multiple agents , each digital signature associating one of the agents with one or more of the content items ; and assigning a score to a first agent of the multiple agents , wherein the score is based upon the content items associated with the first agent by the digital signatures .