French tanker's uniform

Probably 1920s. Note the small beret and rank slide attached to the front of his leather jacket. Any ideas as to the slogan?

"Nain Jaune" ("Yellow Dwarf")? Well the tank is rather small to modern eyes . However the most likely reason for this whimsical name is probably a French card game which dates back to the 17th century but became popular again between the two world wars. Other uses of "Nain Jaune" are (i) a nickname for a legendry female Pope Joan during the middle ages; and (ii) the title of a French literary fairy tale involving an enounter between a beautiful maiden and a small person. Neither of the latter seem particularly likely to have inspired a French tank crew of the 1920s as a name for their vehicle so its probably the cards. I think that U.S. bomber crews during WWII were also prone to personalising their aircraft by painting names and pictures on the hulls.