Dear Friend,
Authorised signatory and power of attorney are entirely different.
Authorised signatory : This is an internal procedural adjustment, some one is authorised to carry on the works on paper and to deliver on behalf of the seniors. This is a delegated power. However, authorised signatory and the power is restricted. In Govt. Sector, some officials are recognised for authorised signatory on cheques. The responsibility squarely rest on those who delegate the power.
Power of Attorney : It is an Act, under the Law Commission of India, the power attorney entails the responsibility on those who are delegated with the power on behalf of some one, this is being registed under the Act (respective Acts), A Chartered Accountant is delegated with the power attorney for the cases on behalf of the owners/organisations, Land dealings are come under power attorney who is authorised to sell on behalf of the land owner, etc., such power of attorney need be registered with the authorities on due formalities. You please find an attachment for power of attorney for your reference.