A notice issued under section 148 having no signature of the AO affixed on it, digitally or manually, would be invalid, and would not vest the AO with any further jurisdiction to proceed with the reassessment under section 147 vide [2023] 451 ITR 27 (Bom).
Importantly this defect is also non curable even in terms of the provisions of section 292B of the Act.
In the consequence any steps taken in furtherance of notice issued under clause (b) of section 148A of the Act and order issued under clause (d) of section 148A of the Act, would also be without jurisdiction, arbitrary and contrary to article 14 of the Constitution of India.
In sum and substance therefore an unsigned notice is a non starter really.