Klaatu Barada Nikto Road Sign.

From the website:

This was the first time I had attempted a prank like this, so I expected the control box to be locked, and the programming functions password-protected. I was wrong. First of all, the control cabinet had no lock. Swinging open its door, I found a deliciously inviting handheld keypad, then took a wild guess and pushed a button labeled STOP. The display on the control box flashed ENTER PASSWORD. I was about to give up in disgust when I noticed that someone had written the password in large Sharpie lettering above the box.

With only a few minutes of road sign hacking, I had programmed an homage to the 1951 sci-fi film The Day The Earth Stood Still, the phrase that was used to stop Gort, the robot in the film, from taking over the world.

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