Dangerous oranges

Sometimes the most seemingly innocuous information can be beneficial in wartime. In 1944 the Americans discovered they need not risk the lives of the French Resistance to discover if the transport links with Spain were still open. All they had to do was find out the price of Spanish oranges in Paris. When the links were cut, the prices went up, when the price went down, it was time to bomb the bridges again! Can you imagine what went through the mind of the resistance fighters when they were regularly asked to provide the cost of oranges?