County road signs in Minnesota Department of Transportation District 3.
Stearns County uses M1-6M for county state-aid highways and M1-X4 for the rest.
Verified by email with the highway department of Stearns County.
Todd County uses M1-6M for only inter-county highways (matching the blue and white rectangular signs).
If the Inter-County sign is not present, M1-X4 is used, even for inter-county highways.
Verified by email with the head of the Todd County Public Works Department.