Short after WWII, France lacked small change. Arming industry had required much metal like copper and the government didn't strike small coins anymore.
In 1920 Édouard Bouchaud-Praceiq invented the money-stamp. A postal stamp was sealed between a slice of aluminum or tinplate and a slice of transparent mica, in order to be used as a substitute for official coins.
Contrary to other tokens of this period, the facial value was guaranteed by a stamp with a fiduciary value (the stamp could even be reused), while keeping the advantage of being protected against damage or deterioration.
The production costs were pretty high: 10 centimes to produce a 5 to 25-centimes coin. These costs were met by companies who used money-stamps for their promotion. The French bank "Crédit Lyonnais" especially used this kind of advertisement (see picture).
Money-stamps stopped circulating in 1924, when French government began producing new coins.
Many different types were produced. Main differences are the stamp value, the background color, and the advertisement on the back. Unfortunately there are very few of each and they are pretty rare nowadays.