Extra context for "What do I do with sign languages?"
All sign languages that I'm aware of use roughly the same sign for the third-person singular pronoun, namely, pointing to that person, or at the locus in the signing space associated with that person if thon is not physically present.
This means that we could on the one hand (heh) assume that all sign languages in history have used this system of indexicality, and that sign languages have always existed wherever deaf people have existed, and that deaf people have existed everywhere humans in general have existed, and therefore not just all of Europe but the entire world has always shared the one unifying gender-neutral pronoun of simply pointing at someone -- at least among those proficient in a sign language. On the other hand, we could also assume that prior to the advent of deaf schools that deaf people might've had village signs in large cities, and otherwise might have had home signs or similar not-quite-languages, and so it's only after the advent of deaf schools that we should start to include Index3 on the map on any large scale. Before then we should only include Index3 if a village sign is attested in a given location, e.g. VLSF is estimated to have had c. 200 signers in Paris in 1750.
Extra context for "How do I find out the 3S pronouns of ancient languages?"
There are a lot of ancient languages that are poorly attested or where the comparative method or internal reconstruction can only get us so far. There are also a lot of languages where I'm not sure if I can't figure out their deals because I'm bad at finding information, or because that information literally does not exist.
The particular thorns in my side Thus Far are the Caucasian languages, Hurro-Urartian, the Anatolian languages, Samoyedic, Ugric, the Paleo-European languages, Armenian, and the Iranian languages. For that matter we might as well add PIE into the mix of mysteries due to the theories that its three-gender system resulted from a split in an earlier animate-inanimate distinction. I'm also somewhat worried that I'd be unaware of some interesting dialectal pronouns throughout history.