Mac OSX: Personalize your login window

I've been a mac user since a very long time. Currently, my main machine is an aged Black MacBook 1st generation. For some, whenever you leave your mac, you will of course leave it to your login window (in Windows, it is known as lock user by pressing Window+L) so that your computer is safe from the wrong hands meaning that nobody can access your computer (your session at least) without your user authentication.

In mac, the only way to allow this is by enabling fast user switching first, from there you click on your fast user switching icon (usually on the top right) and select "Login Window...".

If you want to add more personalized message in the login window such as "This computer is mine", go to the terminal and type the following:

sudo defaults write /Library/Preferences/com.apple.loginwindow LoginwindowText "This computer is mine"

Then try to go to the login window and voila, you will see the text just above the user list. Have fun!