This Decoder Ring was a prize in a Monolith Burger Fun Meal! It can be used to decode any secret message. Well, almost any secret message.
Roger Wilco, who obviously chose to use his mental age when deciding upon his meal at Monolith, obtained one of these Decoder Rings and used it to decode a secret message from the Two Guys from Andromeda, which was embedded in the Astro Chicken game.
The idea of a prize in the Fun Meal comes from the prizes gained in McDonald's Happy Meals.