Can the police search me just for having a patient registry card?
No, not under Montana law. Possession of, or application for, a registry identification card does not alone constitute probable cause to search the person or property of the person possessing or applying for the registry identification card or otherwise subject the person or property of the person possessing or applying for the card to inspection by any governmental agency, including a law enforcement agency.
Michigan law. Possession of, or application for, a registry identification card does not alone constitute probable cause to search the person or property of the person possessing or applying for the registry identification card or otherwise subject the person or property to inspection by any governmental agency, including a law enforcement agency.