Linux: Display or change a pre-login message .

Open file /etc/issue and change the text:

You can use this to add some new infos or ascii image.
The images can be transform into ascii image by using convert image to ascii.
One example to convert a picture into ASCII TEXT,HTML is this website:
The main problem can be if you have escape codes consist of a backslash (\) immediately followed by one of the letters explained below:

\b : Insert the baudrate of the current line.
\d : Insert the current date.
\s : Insert the system name, the name of the operating system.
\l : Insert the name of the current tty line.
\m : Insert the architecture identifier of the machine, eg. i486
\n : Insert the nodename of the machine, also known as the hostname.
\o : Insert the domainname of the machine.
\r : Insert the release number of the OS, eg. 1.1.9.
\t : Insert the current time.
\u : Insert the number of current users logged in.
\U : Insert the string “1 user” or “ users” where is the number of current users logged in.
\v : Insert the version of the OS, eg. the build-date etc.