Set a Lock Screen message with a promotion, personal details, whatever you want

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screenshot thanks to Matt Gemmell
OS X allows you to set a message for the Lock Screen, which appears when your screensaver kicks in or your Mac simply locks due to inactivity. Go to System Preferences > Security & Privacy > General > Set Lock Message to do just that, and use ⌥-Return to create a new line.

Matt Gemmell brought this up as a great idea to promote yourself or a product while attending a conference, or simply as a basic security precaution.

[thanks to Matt Gemmell for permission to use the screenshot]