Quality-of-service (QoS) signaling protocols for mobile ad hoc networks (MANETs) are highly vulnerable to attacks. In particular, a class of Denial-of-service (DoS) attacks can severely cripple network performance with relatively little effort expended by the attacker. We propose a distributed QoS signaling protocol that is resistant to a large class of DoS attacks. The key elements of the scheme are: sensing of available bandwidth, traffic policing, and rate monitoring. The proposed signaling scheme provides QoS for real-time traffic and achieves a compromise between signaling protocols that require the maintenance of per-flow state and those that are completely stateless. The signaling scheme scales gracefully in terms of the number of nodes and/or traffic flows in the MANET. We analyze the key security properties of the protocol and present simulation results to demonstrate its resistance to DoS attacks.