The apparatus includes a first communication device 20 disposed at a control point 14 and a second communication device 26 disposed on the advertising medium 16. The second communication device supplies data for the first communication device, by means of which the presence and integrity of the advertising medium on the vehicle can be checked. Other information bearing on the eligibility of the vehicle for a credit may be included in the data and checked by the first communication device. The apparatus and method also include a device for issuing a credit as payment for the attachment of the advertising medium to the vehicle, provided that the result of the check for the presence and integrity of the advertising is positive.