No person shall expose, distribute, or place any sign, advertisement circular, notice, or statement or display any banner, emblem, or design, within the park except that temporary, freestanding directional signs on the day of an event which will be held within the Park District may be placed in designated locations with the approval of a ranger and must be removed at the conclusion of the event. No such sign may be affixed to any tree or park property, except where authorized by permit.