In fact, in the French Foreign Legion (and in the French Army as well), it is a staff sergeant who is usually the lowest rank to lead a platoon; a sergeant is a rarely seen exeption (see Ranks). This kind of promotion was more common during the First Indochina War (1946-1954) only, due to the lack of senior NCOs and officers back then. That’s maybe the reason why the sergeant of the 1re CSPL wears the Platoon Leader Badge (Brevet chef de section), created in the early 1930s, with different color and military branch insignia for different French Armed Forces branches. The Legion NCO most probably wears that red one made for Infantry, with the grenade. Note that both badges are attached to a single leather fob/backing.

Another photo from the same 1958 collection shows the 1re CSPL commander, Captain Prod’homme who bears a personal fourragère, and other of his platoon leaders: two lieutenants and a senior NCO (an adjudant or adjudant-chef). A nice company (guest-) book decorated with a large unit insignia is seen on the table.

Note that the insignia on the book has a different design of the two Legion colors (green and red) than the badge worn by the sergeant. On the book, the flames of the grenade are in the green field. The same year – in 1958 – Captain Prod’homme sent a letter to Kepi Blanc (the official magazine of the Legion), asking what type of these two badges was correct. According to the captain, for several years, each type had been seen as the only right one by part of the company. The problem originated when manufacturers made both types of the insignia after two different paper designs they had obtained. In his letter, Captain Prod’homme pointed out that as a young Legion officer, he was taught about the Legion colors that “the blood flows on the plain” and that “the burning flames are always above the grass.” Which means that the red should have been above the green, and the grenade flames should have been placed in the red field.