Trolls are passing around an image pretending to be a promotion from Apple that promises to give your iPhone a "retro" look if you set your phone's clock back to 1970. To be fair, since there were no cell phones in 1970, you'll feel pretty retro when you suddenly no longer have one, either.
The image, ones like it (see below), and many trolls leaving comments across the Internet are claiming that if you set your phone's clock back to January 1st, 1970, your phone will get an exciting throwback theme. This ignores the fact that if you truly had a retro PC look, you'd suddenly have to learn basic programming just to access your texts from the command line. More importantly, it bricks your phone (makes it basically unusable) and you'll have to go to the Genius Bar to fix it, which won't be fun or free if your warranty is up.