Explanation:

The Coinage act 2011 which took over Coinage act 1940 says "necessary provisions for inclusion of Government of India one rupee note within the meaning of ‘Coin’ have been consciously incorporated in the Coinage Act, 2011. Further, the RBI, as per Section 24(1) of the RBI Act, 1934, is not empowered to issue bank note of denomination of value of one rupee.
The Re 1 note has the signature of the Finance Secretary to the government of India. This has been so because the one rupee note was reintroduced as a wartime measure in 1940, issued by the Government of India with the status of a coin. Government of India continued to issue Rupee one notes till 1994.