Digitally sign client communications (when possible)
Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options
If this policy is enabled, it causes the Windows 2000 Server Message Block (SMB) client to perform SMB packet signing when communicating with an SMB server that is enabled or required to perform SMB packet signing.
This policy is defined by default in Local Computer Policy, where it is enabled by default.
See Digitally sign client communications (always) for further details about using digital signatures in client/server communications.