I use this for SSH server.
W A R N I N G
THIS IS A PRIVATE COMPUTER SYSTEM.
This computer system including all related equipment, network devices (specifically
including Internet access), are provided only for authorized use. All computer systems
will be monitored for all lawful purposes, including to ensure that their use is
authorized, for management of the system, to facilitate protection against unauthorized
access, and to verify security procedures, survivability and operational security.
Monitoring includes active attacks by authorized personnel and their entities to test or
verify the security of the system. During monitoring, information will be examined,
recorded, copied and used for authorized purposes. All information including personal
information, placed on or sent over this system will be monitored. Uses of this system,
authorized or unauthorized, constitutes consent to monitoring of this system.
Unauthorized use will subject you to criminal prosecution. Evidence of any such
unauthorized use collected during monitoring will be used for administrative, criminal or other adverse action. Use of this system constitutes consent to monitoring for these purposes.
For my console I use this banner.
WARNING: Unauthorized access to this system is forbidden and will be
prosecuted by law. By accessing this system, you agree that your
actions will be monitored and logged at all times.
I found the following document very helpful. SSH Warning Banners