I don't think that they were capable of dropping one, since during war every countries kind of went on a blockage period weren't they?

There could be chance where there were spies sent to the country to steal information but normally weren't they captured and locked down? Since the nationalism, the ideal that whom from what country would have a certain amount of loyalty to that country and would be a higher risk to betray the enemy country?

For example the Japanese American case during WWII that nearly all of them were sent to isolated on an island, the rest were shot and killed. No Japanese were allowed to appear, how could they drop any posters. "I'd rather do wrong to others than allow them to do wrong to me!" - Cao Cao

Propaganda was huge issue back then in both way, spreading and sealing things.