In Hyperledger Fabric, if end users of the application want to keep their private key secret and secure, they would use offline signing. Offline signing involves signing transactions on a device or in an environment that is not connected to the network or the internet. This method ensures that the private key used for signing does not get exposed to the network and reduces the risk of compromise. Offline signing is especially important in scenarios where security and privacy are paramount, as it allows users to maintain control over their private keys at all times.