Overlay networks have received a lot of attention due to the recent wide-spread use of peer-to-peer (P2P) applications such as SETI, Napster, Gnutella, and Morpheus. Through replications at numerous peers, digital content can be distributed or exchanged with high resilience and availability. However, existing P2P applications incur excessive overhead on network traffic. For example, Gnutella, which broadcasts queries to search shared content, suffers from an overwhelming volume of query and reply messages. In this paper, we investigate the issues of trading-off storage space at peers to reduce network overhead. We propose signatures for focussing searches along selected network paths, and introduce three schemes - CN, PN-S and PN-A, to facilitate efficient searching of shared content in P2P networks. With little storage overhead, these signatures improve the performance of content search and thus significantly reduce the volume of network traffic. Extensive simulations based on un...