a vehicle - roof mounting - base , for supporting sign or light elements , that uses vacuum evacuation to adhere the vehicle - roof mounting - base to a vehicle roof . the vacuum evacuation is accomplished by using a continuous , gas impermeable seal between the lower surface of the vehicle - roof mounting - base and the vehicle roof . a vacuum pump then partially evacuates the volume enclosed by the continuous seal , the vehicle roof , and the lower surface of the vehicle - roof mounting - base , providing sufficient retention force to hold the vehicle - roof mounting - base to the vehicle roof .