It also shows a horizontal stroke associated with Siddham vowel letter A that correlates with the dependent forms of the other vowel letters. In Japanese, this stroke is known as the ア点 a-ten "a mark" and is considered to be an elongated form of the 命点 myō-ten "life mark". The myō-ten is the initial brush stroke used in the writing of all Siddham letters. The a-ten is produced by extending the myō-ten to the right. It is not a true vowel sign; it is the headstroke of each consonant letter.
My unconfirmed hunch is that the Siddham analysis of the a-ten arose as a way of explaining the inherent vowel /a/ possessed by every consonant letter. All Indic vowels have both independent and dependent forms, except for the letter A, which has only an independent form. The a-ten raises several philosophical questions regarding the sound and forms of letters: How does one capture this inherent sound, which is part of the phonetic identity of each consonant letter, but which is graphically unmarked? Is it contained somehow in the letter form? If so, where in the glyph does it reside? As it represents the initial brush stroke used for writing the vowel letter A, it may be said to contain the graphical and phonetic essence of the letter.
I raise the matter of the Siddham myō-ten and a-ten because it is significant from an ideographic perspective, as are the other elemental strokes identified in pedagogical texts. I am currently investigating the potential of encoding these elemental strokes, which I mentioned in my Siddham proposal as being out of scope for the basic encoding. I welcome any information on the myō-ten from users familiar with its philosophical interpretations and its use in Siddham pedagogy.