Verification of tax returns: authorised signature requirements determine validity and prevent invalidation by later processes. Verification requires the taxpayer or an authorised person to sign the income tax return; individuals may delegate signing only by a valid power of attorney attached to the return. Specific categories (HUF, companies, firms, LLPs, local authorities, political parties, associations) must have their prescribed officials sign, with alternates where the primary officer is absent or incapacitated. An unsigned or unverified return is invalid and not curable by post filing processes; recognised non handwritten marks such as thumb impressions may be acceptable.