When you ride the subway every day, your eyes tend to adjust to signs posted everywhere. These safety and courtesy precautions all just sort of blend together after a while to become wallpaper that you don't even notice, despite the fact that gaining the notice of passersby is a sign's sole intent. Anyone paying extra attention on the London Underground recently, though, would be rewarded with an unexpected blast of absurdity.
Some as-yet anonymous group has taken the hacking skills of the Syrian Electronic Army, and manifested them in physical reality. Lately, the signage on the London train system has focused less on safety and courtesy than it has on some candid opinions about different areas of London, as well as incisive commentary about the way people tend to studiously ignore each other in public transit.
Some of the sign-disruptions target the progress maps that show commuters which stop they are currently passing. An actual image of a pregnant woman, a person with a baby, and an old man with a cane, has a message asking people to give up their seats for "the overweight, the conjoined, and snake charmers." Other messages focus on the avoidance of eye contact.
Ironically, the very same signage that people tend to block out due to its glaring familiarity has (undoubtedly briefly) become means to salvation from the very same boredom it usually promotes. Have a look through more of the images in the slides above.