I was doing a bit of reading up about illustrators in France pre war: essentially they were hired in contract by publicity 'agencies', much like record labels today. They were quite poorly paid and rarely allowed to sign their works. Some of these posters sell for good four figures now. Kinda sad to think of the ordinary artist holed up in a Parisian garrett, toiling away with inks at 2am, knocking out dazzling illustrations like this by gaslight!
This one from the WALL Agency. 'She climbs everything'. This one is signed 'Mich'.