Mont. Code Ann. § 60-6-102
Notice of encroachment
60-6-102 . Notice of encroachment. (1) Notice to remove an unpermitted encroachment, specifying the width of the highway right-of-way and the place and extent of the encroachment, must be given to the person erecting or maintaining the encroachment.
(2) Notice must be given in the following manner:
(a) in writing by certified mail sent to the person's business or personal address or by personal service; or
(b) if the person's address cannot be found, by posting it on the encroachment.