Prices and wages, for the most part, were frozen in the United States. The most recent pre-war German visitor would not have been aware, nor would a Nazi provocateur have cared, that the U.S. Postal Service was permitted a one cent increase for airmail.
Like gas rationing, the increase was not profiteering on part of the government but to discourage people from using airmail except when it was absolutely necessary.
During the Ardennes offensive, known as the Battle of the Bulge, Nazi infiltrators disguised as American soldiers were revealed when small secrets were asked.
Among the small secrets, that most American males would know, were 'Who won the World Series?' or 'Who is Jiggs?'
The 1944 World Series was won by the St. Louis Browns, and Jiggs and his wife Maggie were a popular Sunday print cartoon known as Bringing Up Father. (Note examples above and below)