On this special Secrets of D.C. edition of Mysteries at the Museum Host Don Wildman investigates a standard-issue US Postal Service mailbox at the International Spy Museum in Washington D.C. This commonplace item was the centerpiece of one of the most devastating Cold War spy cases. Encased at the Ford's Theatre Museum in Washington, D.C. visitors can admire a seemingly primitive weapon - brass knuckles - that was used to protect one of America's most celebrated presidents against a murderous plot. And at the Newseum in Washington D.C., a simple five cent nickel sliced in half was used as an unlikely tool to conceal international secrets.