Your start-up will be constituted under Private limited Company. According to Section 21 of Companies Act, 2013, a document or proceeding requiring authentication by a company; or contracts made by or on behalf of a company, may be signed by any Key Managerial Personnel or an Officer or Employee of the company duly authorised by the Board in this behalf.
An authorized signatory or signer will be the person who will be given the right to sign documents on behalf of your start-up aka Pvt Ltd Co. As the directors of the company, any of the two directors can become the authorized signatory of the Company. You can decide on an authorised signatory among the directors by way of a board resolution. Pvt Ltd. he authorized signatory can be authorized only by the Board. Pvt. Ltd Co. having share capital of more than Rs. 5 crores needs to appoint whole time Company Secretary as a mandatory provision.
Along with Sections 21 read with Section 22 of the Companies Act, 2013, Memorandum of Association (MOA) and Articles of Association (AOA) of the company need to be referred for appointing an authorised signatory which have to be decided by the Board among one of the directors of the Company.