The correct answer is: The President of India.
The signature of the President of India appears on the obverse (front) of all Indian currency notes. The Governor of the Reserve Bank of India signs the reverse (back) of all currency notes. The Finance Minister of India is not responsible for signing currency notes. The Finance Secretary of the Government of India is responsible for the printing and distribution of currency notes, but does not sign them.
The signature of the President of India on currency notes is a security feature that helps to prevent counterfeiting. The signature is unique to each President and is difficult to forge. It is also a symbol of the authority of the Indian government.