Fake plate (there is no 18th month - these ciphers are on seasonal plates).

In America and also Japan it's stylish to put German plates under the actual ones.
In the USA there are even companies, specialized in fake plates for that purpose.

For my crazy Japanese VW-Audi friend I've organised several invalid old plates, which he sold to freaks for German cars. Most popular were WOB, M and S, also IN