This poster has a clear imagery - deposit your gold and strengthen the defense!
Here you see a German soldier with the classic pickel hood or "pickelhaube" suddenly being attacked by a large gold coin with le coq gaulois i.e. "the Gallic rooster", which early on became an unofficial symbol for France. The rooster's name is commonly known as Chantecler, and dates back as far as the Gauls of the 500s. The rooster was stamped on the reverse side of French 20-franc gold coins during the years 1899 to 1915. The rooster is still a popular mascot at sporting events and is found on many French monuments of the First World War.
This way of financing the armed forces through the public essentially functioned in the same manner as the more common war bonds where, at the eventual successful end of the war, their invested funds were paid back plus an attractive interest rate.
Probably very few during these times had an abundance of money, but the reasoning here was that many could instead pledge rings and jewelry that one could, for sentimental reasons, otherwise be unwilling to sell.