I recently came across an anecdote that claims Firmato (meaning "signed by") became a popular Italian name in the wake of WW1. The story goes that illiterate peasants read the Bollettino della Vittoria and mistook its ending of Firmato Diaz (signed by Diaz) as General Armando Diaz's actual name, and thus many tried to name their children after him.
On the face of it, this appears to be an urban legend and I find it hard to believe, but it's the first I've heard of this. I can't find any evidence of Firmato appearing in Italian name collections. Any searches for the name itself only turn up other accounts of this same story. The images of the Bollettino della Vittoria I can find also all seem to have different endings, many of which would disprove this story, but at least some of them do have the alleged "Firmato Diaz" ending, so I'm guessing the text varies slightly based on the individual plaques where it's displayed. It was apparently put on display in every town hall and military barracks in Italy after the war, so that's a lot of room for variation.
Right now, I'd right this off as fiction, but I was wondering if someone with more expertise in Italian history might be able to shed some light on it.
Far from being conclusive evidence that no one was named "Firmato", a search within this non complete database of individuals involved with WW2 shows no recorded individuals with that name. Someone born around 1919-20 would have served in WW2 - nonetheless it is still a small size sample compared to the whole of the male population, but its should give some results if the name was somewhat popular.
Rare and uncommon names are not unheard of though, and their absence from records may not be by itself indication of total absence - that is, the Italian local authorities followed usually a rule of thumb in recording names; to either use already common names, or names of catholic saints or, at times, accepting "literary" versions of the requested name.
This fact would not prevent the person to go by their chosen name in everyday life. Now, faced with the request of "Firmato", the registry clerk would have likely understood the mistake and its reason and suggested the alternatives: Firmino, name of two catholic saints, (recorded 11 times) or Fermo, a quite common popular name, which had been chosen as the name of the male protagonist of Alessandro Manzoni's Promessi Sposi before being turned into Renzo in later drafts. Fermo gives 114 results.
It is indeed possible that one choose to go by "Firmato" despite being recorded as Fermo or Firmino. And records would show no evidence of that. The best way to find some would likely be to go through obituaries of men named Fermo and look for a
Fermo "Firmato" ...
as usually happens with men going by a common name instead of their recorded one. You can give it a try here but so far I have found none.
As for the presence of the "signed Diaz" ending, that's indeed quite common.