Nickel contains a microdot that is only one square millimeter in size. It contains a code or cipher used by KGB agents during the cold war. This microdot is a reproduction of the microfilm found in the famous nickel that was mistakenly given to a paperboy in 1953 from whom the FBI obtained it. From this coin, the microfilm and information obtained from defecting agents, an entire Russian spy ring was broken. This was probably the biggest cold war win for the US in the world of microdots to that point. Visit the FBI website for the entire story as they tell it best.