What gave rise to the manual alphabet for Latin characters in Japanese Sign Language?

Question

I am aware of the fact that this question is rather specific, but anyway I would like to give it a try.

Japanese Sign Language has three manual alphabets: one for representing kana-characters, and two for Latin characters. The first Latin-character manual alphabet is adopted from American Sign Language (ASL) with minor adjustments. My question concerns the second Latin-character manual alphabet which I call "JSL Latin manual alphabet". All three can be viewed here: http://www2s.biglobe.ne.jp/~kem/yubimoji/yubi-gaz.htm

They are used according to the purpose. According to my personal experience, when spelling a string of Latin letters such as the name of an internet page or the title of a movie, most commonly signers would use the ASL-based manual alphabet. On the other hand, when the letters form an abbreviation such as "NHK" or when a single character is combined with numerals such as in "B8" (designating a subway exit number), signers would tend to use the JSL Latin manual alphabet. I also noted an age difference: Younger JSL signers are more apt to use the ASL-based manual alphabet while the older generation prefers the JSL Latin manual alphabet. Still, both are presently in use.

My question concerns the JSL Latin manual alphabet (i.e. the last one on the page above). It is perculiar as it at times uses one hand, at other times both hands. I have checked a list of manual alphabets of the world (http://www.michaelszczepanski.de/fingerabc.html), but it does not resemble any other manual alphabet that I have seen so far.

When and where was it introduced into the Japanese Sign Language and what is it based on?

Answer 1

Atypically for a sign language, many JSL morphemes are derived in some way from the writing of the society's spoken language (I could suggest that's because Japanese has quite an unusual way of writing, but that's by the by).

For example 井戸, which means a well (where water is drawn from under the ground) is signed by holding the index finger and middle finger of both hands crossed so that the fingers resemble 井. Similarly, the word ルール (which means a rule), is signed by its striking appearance, with each hand fingerspelling (and also resembling) a ル. Another example is the syllable へ which is signed with the thumb and pinkie extended, and hand pointed downward, as though to suggest the shape of the letter へ.

Many of the JSL Latin manual signs seem to be derived in the same way from the Latin alphabet.

Also, the JSL Latin manual alphabet does not seem to have been imported or exported, or else we would see something similar in neighbouring countries, for example Taiwan or Korea (which each have related sign languages) or USA, from which JSL borrows quite heavily.

These two things lead me to conjecture that the JSL Latin manual alphabet was innovated in Japan sometime before the ASL manual fingerspelling alphabet was introduced. Unfortunately, JSL history is quite scantily documented, so that it's hard to find any sources.