Here you go:
IC 9-30-2-2
Uniform and badge; marked police vehicle
Sec. 2. A law enforcement officer may not arrest or issue a traffic information and summons to a person for a violation of an Indiana law regulating the use and operation of a motor vehicle on an Indiana highway or an ordinance of a city or town regulating the use and operation of a motor vehicle on an Indiana highway unless at the time of the arrest the officer is:
(1) wearing a distinctive uniform and a badge of authority; or
(2) operating a motor vehicle that is clearly marked as a police vehicle;
that will clearly show the officer or the officer's vehicle to casual observations to be an officer or a police vehicle. This section does not apply to an officer making an arrest when there is a uniformed officer present at the time of the arrest.
As added by P.L.2-1991, SEC.18.
Now, in Maynard v. State (I think), it was held that if no contact between the officer and the defendant occurrs, that doesn't apply. For example, an officer views someone driving, and he knows for a fact that person's driving privileges were revoked. He can draft an information, probable cause affidavit, and a traffic ticket, and drop them off at the prosecutor's office for further action. In this type of situation, he wouldn't be performing a traffic stop.
Look what two minutes on Google reveals. Google is your friend.
so he can be out of uniform but in a marked car also?