Here are images of the four airmail semi-postal (charity) stamps in a set depicting various Olympic Games sports, designed by French artist Pierre Gandon (1899-1900), engraved by several French engravers, and issued by Monaco in July, 1948, Scott Nos. CB7-CB10.
Rowing, engraved by Charles Mazelin (1882-1968).
Skiing, engraved by Achille Ouvré (1872-1951).
Tennis, engraved by Raoul Serres (1881-1971).
Sailing, engraved by Charles-Paul Dufresne (1876-1956)..