I don’t setup new laptops often enough to remember how to add a message to the lock screen on Mac OS, so I’m leaving a reference here for it. Apple has a support page describing the steps. Just in case that page goes away, the steps are:
– Go to System Preferences and click on Security & Privacy.
– Click on the lock icon in the bottom left corner, provide your username and password.
– On the General tab enable “Show a message when the screen is locked”.
– Click on Set Lock Message.
– Type in your message, then click OK.
This is an easy way to leave a note on the screen about who to contact if your laptop is lost.