Hello Fred,
...immediately this ring puts me in mind of the Nazi Totenkopf (literally "death head") Rings . There were a number of different style including some called anti-Partian rings. These were worn by the units of the German SS that were tasked with hunting down the underground French resistance. The brutality of the SS toward French citizens, and of the French resistance toward German soldiers escallated through the occupation with unspeakable acts committed by both sides.
More of these rings here: http://seifukuwatch.kir.jp/english_ring_toppage.htm
Though as BobDylan mentioned, the rooster is a cult symbol, but is used for other symbolic purposes as well. One of these happens to be the national emblem of France:
>>The Gallic Rooster (Coq Gaulois), or cockerel, is the French national emblem, as symbolic as the stylised French Lily. From the very roots of French history, the Latin word Gallus means both "rooster" and "inhabitant of Gaul". The French rooster emblem adorned the French flag during the revolution. With the success of the Revolution in 1848, the rooster was made part of the seal of the Republic. In 1899, it was imbossed on a more widespread device, the French 20 franc gold coins.<<< During the WWI, the rooster became a popular symbol in France in opposition to the German Imperial Eagle. The Gallic cockerel appears on government seals, and was the symbol used by the French Resistance in WWII as a reminder of the resilience of the French people, bolstering their commitment to resist. It is still used for French sports teams
As you mentioned, this ring looks homemade. What is curious about that, is the skull and roosters look manufactured not homemade--the roosters especially appear to be cut out of something that was already made. Since the roosters are copper, and the fellow who made the ring had at least two of them and was not concerned with altering them, there's a good possibility they came from something common place like a low denomination coin.
The closest I could find was this, however
From France, 10 Francs 1950-1959 (aluminum-Bronze)
Close but no cigar...
I have a hunch that this ring was possibly made by a Frenchman, during or shortly after the war, that it was modeled after the Nazi rings worn by the SS in occupied France, as a patriotic statement that a Frenchman too could be ruthless when required. So far, nothing but a hunch though and nothing to confirm this.
It would be interesting if the source of the copper roosters and skull could be found.
I dunno about being a cult ring as that kind of thing usually has strange writing and symbols and the roosters kinda look more suited to a box of Corn Flakes than to a blood sucking orgy.