The concrete Garden of Eden sign. Blink blink blink goes the radium metal embedded in the concrete. Other trace elements, which emit odors for millions of years in the same way that radioactive materials emit radio without stopping (transmissions moving from star to star, never quite loud enough to hear, never quite soft enough to block) are embedded under every other letter. Plus, the whole thing is lit at night (or would be, if night ever came... parts of the general machinery are broken).