The login window appears when you're logged out of your user account. Depending on your Security & Privacy preferences, it may also appear when you wake your Mac after sleep or screen saver begins. In the example below, "Welcome to my Mac" is a custom lock message.
How to set a lock message
- Choose System Preferences from the Apple menu (), then click Security & Privacy.
- Click and enter your administrator name and password.
- In the General tab, select "Show a message when the screen is locked," then click "Set Lock Message".
- Enter your message in the text field. Click OK.