Signature

very interesting question.

so far i know, signature and left thumb impression are alternative. sorry no citation so far seen.

Yes as per Income Tax Act, 1961 & also as per the general clauses act. but citation sorry i dont have .

I to also required the whole case & not only the citation dear Jurist also the judgment if available than get apex court judgment ok.

Best of Luck.

God Bless U All.