you may have came across above statement specially when vulnerability scanning. nessus scanner identified above issue by the plugin ID 57608 as below

Severity: Medium.

ID: 57608

File Name: smb_signing_disabled.nasl

Version: 1.18

Type: remote

Family: Misc.

this issue occurred when SMB traffic or server is not signed so an unauthenticated remote attacker can exploit or launch a MIM or Man -in- Middle attack against the SMB server.

the vulnerability can be fixed by enforcing SMB signing from a Group policy for Clinet and server.

GPO Location : Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options

Fore more Details read below.

https://docs.microsoft.com/en-us/windows/security/threat-protection/security-policy-settings/smbv1-microsoft-network-server-digitally-sign-communications-always

https://docs.microsoft.com/en-us/windows/security/threat-protection/security-policy-settings/microsoft-network-server-digitally-sign-communications-always

Happy Fixing :)