Indian Evidence Act, 1872
47. Opinion as to handwriting, when relevant
When the Court has to form an opinion as to the person by whom any document was written or signed, the opinion of any person acquainted with the handwriting of the person by whom it is supposed to be written or signed that it was or was not written or signed by that person, is a relevant fact.
The question is, whether a given letter is in the handwriting of A, merchant in London.
B is a merchant in Calcutta, who has written letters addressed to A and received letters purporting to be written by him. C is Bís clerk, whose duty it was to examine and file Bís correspondence. D is Bís broker, to whom B habitually submitted the letters purporting to be written by A for the purpose of advising with him thereon.
The opinions of B, C and D on the question whether the letter is in the handwriting of A are relevant, though neither B, C and D ever saw A write.