I can find some information online regarding signing in Europe, but nothing on Asian sign history. I tried to ask r/askscience but to no avail. Anyone here with more knowledge? Thanks in advance for all replies! :)
Signed languages are natural languages, so in many cases their development in Asia is the same as their development in Europe. Where there is a large enough concentration of deaf people to develop a manual language, it happens naturally.
There are a few countries, though, where naturally developed sign languages are no longer in use. Modern Thai Sign Language is heavily influenced by American Sign Language, as educators who had been trained in the US established schools for deaf children in Thailand. ASL merged over time with existing sign languages in Thailand to create the Modern Thai Sign Language in use today. (This is actually how ASL was created, too - the natural amalgamation of French Sign Language with existing signed languages in the US.) Filipino Sign Language followed a similar path to Thai.
Taiwanese Sign Language and Korean Sign Language are both heavily influenced by Japanese Sign Language, from the period when Japan occupied these areas. There has been significant departure from JSL in both countries, but the influence is still visible.
Edit: Coming back with some other resources now that I'm not on mobile.