County road signs in Minnesota Department of Transportation District 4.
Douglas County both solely uses M1-X4 signs and has an inter-county highway. This puts it at the (almost) unique position of having a blue inter-county sign beneath the white M1-X4 sign.
Pope County uses M1-6M signs on all roads handled on a county level (including CSAH highways),
but state highways use M1-X4 signs.
Verified by contacting via online form the highway department of Pope County.
Road sign patterns seem to match that of Pope County. This is reasonably logical as the two counties are adjacent.