To an SSH legal message, SSH into server and login as root.

At command prompt type:
Enter your message, save and exit.
Note: I use the following message...

ALERT ! You are entering a secured area ! Your IP and login information
have been recorded. System administration has been notified.
This system is restricted to authorized access only. All activities on
this system are recorded and logged. Unauthorized access will be fully
investigated and reported to the appropriate law enforcement agencies.

This System Has Been Secured By Go4ws.com

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جزاك الله خير ..

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بو مُجَاهِد