Overlay networks have received a lot of attention due to the recent widespread 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 to use signatures for directing searches along selected network paths, and introduce three schemes, namely complete-neighborhood signature (CN), partial-neighborhood superimposed signature (PN-S), and partial-neighborhood appended signature (PN-A), to facilitate efficient searching of shared content in P2P networks. Extensive simulations are conducted to evaluate the performance of our proposal with existing P2P content search methods, including Gnutella, Random Walk, and Local Index. Results show that PN-A gives much better performance at a small storage cost.