The image is of a poster for the 1937 Paris World Exhibition. Recognize any of the flags? (Answer below the fold).
These are not national flags. A reader at Poemas del rio Wang offers the correct answer:
They are international maritime signal flags. The front tier reads, from top to bottom: P-A-R-I-S. In between those letters, the next tier back (of penants) reads: 1-9-3-7. Beyond, it's more difficult, the swallow-tail shapes should be distinctive of signal flags, rather than national ones, but I do not find their patterns in memory or any reference guide that I can find.