I have seen those in multiple countries, and couldn't really say there is any correlation with friendliness. But they do have managed to vastly improve my mood

I have seen those in multiple countries, and couldn't really say there is any correlation with friendliness. But they do have managed to vastly improve my mood, via a different sort of mechanism: when I'm being treated rudely, I tend to linger at the machine, usually waiting for fellow passengers to clear security. During that minute or two (or five), I train my Nintendo skill on the :( face. My high score must be in the thousands. They probably filter out such data. But maybe not–I kind of prefer not to know. I get lots of cheeky smiles from other travellers noticing me, so the happiness even spreads. Only got yelled at by security once.