French stock-car race poster, 1954

The poster isn't dated; 4 July was also a Sunday in 1948, but we think it's 1954.

In the U.S. a stock car means any production-based automobile that has not been modified from its original factory configuration used in racing, In the U.K., however, a stock car is often stripped of unnecessary fittings and specially strengthened against collisions for competing in what in the U.S. is called a demolition derby.  It seems the French use of the term is the same as the British.