You may use the following example as a Red Hat Enterprise Linux (RHEL) 7 message of the day (MOTD). This file is located at /etc/motd.

#########################################################################
# For Authorized Use Only #
# #
# Activities on this system are subject to being monitored #
# or recorded for all users, authorized or unauthorized. #
# Use of the system is considered consent to such monitoring. #
# Any evidence of possible criminal activity may be provided #
# to law enforcement. #
# #
#########################################################################