If you want to have a shortcut with for locking the screen, but with prompt for lock message, here’s what you need to do:

1. Go to Settings -> Keyboard, then click on Keyboard shortcuts tab

2. Click on Add custom shortcut button, and enter the following command:
   Shell

   python /usr/lib/cinnamon-screensaver-lock-dialog/cinnamon-screensaver-lock-dialog.py

   1 2 3

   python /usr/lib/cinnamon-screensaver-lock-dialog/cinnamon-screensaver-lock-dialog.py

   example:
   

3. Click Add and then assign it a shortcut.
   For example, the default lock screen shortcut is Ctrl+Alt+L. For the one with prompt, you can assign Ctrl+L.
4. You’re done.
   When you want to lock your screen with a custom “away” message, just press the shortcut you assigned (Ctrl + L)