De-registration or export plates
A vehicle leaving Germany is either de-registered and transported on a closed truck, or fitted with short-term export plates (Ausfuhrkennzeichen) with matching insurance if it will be driven out.
Customs declaration
For destinations outside the EU an export declaration is filed and stamped; the confirmation is your proof of export and is usually required for VAT treatment.
Documents that travel
The transport file should contain invoice, registration documents, export confirmation, condition report and photographs taken at loading.