When I was a kid in the 70s, you could listen to distant shortwave stations and if you heard them on a certain time and freq, you could send a note and get a postcard to collect. So we picked up Moscow and thought that would be cool for the collection. We wanted to make sure we weren't going to get in trouble or a watchlist (McArthy was very fresh on our minds) so we called the FBI office first; they were amused we'd ask.

https://en.wikipedia.org/wiki/QSL_card