Section crpc 91(1) - can be issued only by sho or even by si level io ?

Notice issued by IO u/s 91 Crpc is valid if, if it is endorsed by SHO.

And if not ensdored and only IO Stamped and signed ? Is that considered as malpractice ? Can a case be filed against the IO basis that ? 

Both the Court  and SHO can issue notice u/sec 91 Cr.P.C. Since I.O is authorized by SHO to investigate matter so he can also issue notice u/sec 91 Cr.P.C.and that is perfectly valid.

Section 91(1) cr.p.c. 

Whenever any Court or any officer in charge of a police station considers that the production of any document or other thing is necessary or desirable for the purposes of any investigation, inquiry, trial or other proceeding under this Code by or before such Court or officer, such Court may issue a summons, or such officer a written order, to the person in whose possession or power such document or thing is believed to be, requiring him to attend and produce it, or to produce it, at the time and place stated in the summons or order.

From the above it is clear that officer in charge of the police station can only send the summons uner section 91 cr.p.c.. The Nagpur bench of the Bombay high court has noted that the police officer “committed serious error.” In its judgment dated October 5, the bench headed by Justice  VM Deshpande and Justice Amit Borkar noted that the police officer “has committed serious error in law by issuing notice under section 91 cr.p.c. when essentuial ingredients of the section 91 of the code are not complied with.

The high court has pointed that the IO has got no power to send notice under section 91 cr.p.c., and that this action was totally ultra vires of his powers vested under cr.p.c. 

If you are affected by such action of the IO you can  raise objection and protest the same 

Dear @T Kalaisalvan Sir,

Can you share the judgement link please 

Yes I will certainly share it but you may have to send an email to my email address which is available in this forum.

Sir cannot see your email. Can you paste it here sir ?