WWII Monopoly games had real "Get Out of Jail Free" cards

From the Wall Street Journal:

The board game "Monopoly" served allied prisoners as a real-life tool to get out of jail during World War II, says Brian McMahon in Mental Floss, a magazine of farflung trivia.

In 1941, the British secret service asked the game's British licensee John Waddington Ltd. to add secret extras to some sets, which the Red Cross delivered to prisoners of war. These included a metal file, compass and silk maps of safe houses (silk, because it folds into small spaces and unfolds silently). Even better, real French, German and Italian currency was hidden under the game's fake money. Soldiers and pilots were told that if they were captured they should look out for the special editions, identified by a red dot in the game's "Free Parking" space.

Of the 35,000 prisoners of war who escaped German prison camps, "more than a few of those certainly owe their breakout to the classic board game," says Mr. McMahon.