You can display a custom policy banner to be displayed at the login window on a macOS system and forces a user to accept it. This is different from setting a login screen message that doesn't require any user interaction.
Create the policy file and its security permissions
In this step, we create the policy banner text file and set the security permissions so that everyone is able to read it.
sudo touch /Library/Security/PolicyBanner.txt sudo chmod o+r /Library/Security/PolicyBanner.txt
Modify the contents of the banner
Run the following command to open the policy banner file with Nano. This will allow you to add your policy text. After you're finished, close and save the file, then reboot the system.
sudo nano /Library/Security/PolicyBanner.txt
Remove the policy banner
Run the following command to delete the policy banner text file. This will stop is from showing up at login.
sudo rm /Library/Security/PolicyBanner.txt