At all times when a building or similar structure is in motion upon any street, alley, sidewalk, or public property, the permittee shall maintain flag persons at the closest intersections or other possible channels of traffic to the sides, behind, and ahead of the building or structure. At all times when the building or structure is at rest upon any street, alley, sidewalk, or public property the permittee shall maintain adequate warning signs or lights at the intersections or channels of traffic to the sides, behind, and ahead of the building or structure.