If you’d like to change the message displayed before logging in to the server
sudo nano /etc/ssh/sshd_config
And add (or uncomment) the line
/etc/banner can be whatever file you want.
Now edit the file you referenced, for example
sudo nano /etc/banner
And enter your welcome message.
You may need to restart sshd before your changes take effect
sudo /etc/init.d/ssh restart
If you want to change the message displayed after logging in edit
sudo nano /etc/motd
Now you can put whatever you want to display, e.g.
_ __ _____| | ___ ___ _ __ ___ ___ \ \ /\ / / _ \ |/ __/ _ \| '_ ` _ \ / _ \ \ V V / __/ | (_| (_) | | | | | | __/ \_/\_/ \___|_|\___\___/|_| |_| |_|\___|