A series of ads for Samaritans of Singapore illustrate how people who suffer from depression often mask their real state. The graffiti, expressed in ambigrams, says something completely different when turned upside down. See more examples at Laughing Squid. Link
That took me way longer to decipher than it should of. I kept thinking the first one read "areht" (great) and upside down was "syslit" (myself). Guess I need more coffee...
Abusive comment hidden.
(Show it anyway.)