At all times when a building or similar structure is in motion upon any street, alley, sidewalk or public property, the permittee shall maintain flagmen 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.