Whizbang Dustyboots
Gnometown Hero
Bizarrely, there doesn't seem to be a way to easily find languages in the 2024 PHB via D&D Beyond, either by looking at the table of contents or the search engine. Did they remove that info from the book for some reason?
EDIT: It's under Creating a Character in chapter two, although the site's search engine doesn't seem to be aware of it: 2024 Player's Handbook - Marketplace - D&D Beyond
In any case, "Common sign language" is described as a standard language native to Sigil (as is the Common language itself). The suggestion is it's more widely spoken than Abyssal, Celestial, Deep Speech, Druidic, Infernal, Primordial, Sylvan, Thieves Cant and Undercommon.
So if more characters know sign language than Thieves Cant, I think it's fair to say that lots of NPCs must know it.
EDIT: It's under Creating a Character in chapter two, although the site's search engine doesn't seem to be aware of it: 2024 Player's Handbook - Marketplace - D&D Beyond
In any case, "Common sign language" is described as a standard language native to Sigil (as is the Common language itself). The suggestion is it's more widely spoken than Abyssal, Celestial, Deep Speech, Druidic, Infernal, Primordial, Sylvan, Thieves Cant and Undercommon.
So if more characters know sign language than Thieves Cant, I think it's fair to say that lots of NPCs must know it.