Idaho Code § 18-7029
It shall be unlawful for any person to erect, install, attach or paint, or cause to be erected, installed, attached or painted, election posters or signs upon public or private property, real or personal, in the state of Idaho, without permission from the owner or occupant of such property, and it shall be unlawful for any person to place or leave any literature or other political, promotional or sales materials upon public or private property, real or personal, in the state of Idaho when the owner or occupant of such property, by a sign conspicuously posted on the property, or by other written or audio communication to such person, has forbidden the placing or leaving of literature or other political, promotional or sales material upon that property. Provided, however, that the granting of such permission by any public utility company on behalf of any candidate for public office shall constitute the granting of like permission by such public utility company to all other candidates for the same public office. Any violation of this section shall be a misdemeanor.
Idaho Code § 18-7029