‘Don’t you believe it!’ was a radio program back in the mid to late forties. This program was run by Toby Reed. I listened to a program of it… In the beginning of the show they list off a number of trivia type things, and say if you believe so and so … Don’t you believe it! then goes on to explain what really happened in a kind of documentary style.
I myself was quite curious, knowing that Tom and Jerry and other cartoons were made during world War II at first I thought it might have been a reference to Winston Churchill telling the British not to fear and ‘don’t you believe it’ for the propaganda being sent by the German’s of that time.
So look it up , could be fun - the radio show was called ‘Don’t you believe it’ I have seen reference to programs in 1946 and 1947
On a side note their chef sponsor seems to have been Almond Roca , a confection made by Brown & Haley , actually looked this up and they are still around today , the company originated in 1912.