Psychopaths aren't only in the movies. There are many psychopaths in the world, most of whom hide their true nature very well. They are often experts at masking their predatory behavior; a psychopath can be a wolf in sheep's clothing. And, sad as it may be, that soft and warm exterior quickly gives way to evil intentions.
This design, by Jordan Bouma, is a reminder to be on the lookout for people who disguise their bad intentions. It reminds you to make sure you really know someone before you trust them- to be aware of all the people who hide their abusive natures with friendly behaviors and big smiles.