Most of these do not have
French
acceptance marks but went to the French anyway. Only the early war guns were marked for the most part. As the war progressed, these little extras were too time consuming. I have one Ruby. Made in Spain, sold to France, captured by the Germans, put into a Polish holster and brought back by a US soldier. I've since picked up a proper French holster for it, they cost nearly as much as the pistols do. The Polish VIS holster was a nice bonus. I'll keep it for the story but without papers, that's all it is.
"Gabilondos y Urresti was the original creator of the 9-shot ruby model in 1914. Upon receiving the initial French armed forces contract in 1915, it became the prime contractor and most important company in Ruby pistol manufacture. These pistols sometimes have a GU in an oval marking on the left grip tang and magazine marking." Spanish Handguns by Gangarosa
Your handgun is not one of the earliest models. The company moved from Eibar to Elgobar sometime after the initial production started, perhaps they needed more room for the government contract. The company still exists as Lhama Gabilondos y Cia It is pretty well guaranteed to be a French contract pistol as they could not keep up with the demand the French required.