Welcome to Germany! 
After your arrival at Dusseldorf international airport, you will collect your luggage and will go through customs. Upon your arrival in the main lobby, you will find your driver at the official meeting point, as shown in the pictures. 
You will find this meeting point at the stairs/escaltators between gates 2 and 3, across from the HERZ and Europcar rental car establishments. (Walk right when arriving at gate 1 & 2. Walk left when arriving from gate 3, 4 or 5.)