The Windows SMB server must be configured to always perform SMB packet signing.
The server message block (SMB) protocol provides the basis for many network operations. Digitally signed SMB packets aid in preventing man-in-the-middle attacks. If this policy is enabled, the SMB server will only communicate with an SMB client that performs SMB packet signing.
How this relates to the STIG checklist: STIG vs SCAP benchmark.