I post this with the caveat that the linked article may or may not work. The usual paywall by-passers don't function for some of the bigger publications and the Wall St. Journal is one of them. 

But that newspaper had a short article on Thursday that was something I'd never heard before and I love learning about stuff like this. 

It stated that car radios in the U.S. back during the Cold War days had specially marked triangles on the dial located at 640 and 1240. Why? At the time, there was a real fear the Russians would launch an attack in the U.S. (given this past week, it appears some things never change!) So radio manufacturers were told to mark those positions on all radios, so it would remind panicked listeners where to tune in a hurry in case the Soviets dropped a bomb on America. 

Those two frequencies had been chosen as the go-to spots on the dial to update emergency reports and what listeners would need to know in the event worse came to worse, with all the other stations expected to immediately sign-off during the crisis.

"This was part of Conelrad, an acronym for “Control of Electromagnetic Radiation.” In the event of a Soviet air attack, all broadcasts would go silent except for official emergency instructions over the government’s special network. The triangles, simplified versions of the Conelrad logo, were intended to help citizens, nervously hand-adjusting their radios, to find the proper spot quickly."

I have no idea if Canada did the same thing, but I'm guessing we didn't since I have no memory of it and the system would not have been in place here.

The one thing I don't understand about this, though, is why they would choose 1240. It's one of the worst propagating frequencies on the AM dial, assigned as a local status without much range, and it wouldn't tend to reach very far if people needed to tune it in. 

Still, what a timely and fascinating bit of history trivia that disappeared when the Cold War finally got a lot less frigid. 

The Cold War on the Radio Dial