Attached below is the Numberplate used for this season and to be used in every skin this season, and also the Safety Car and Rescue Car skins used this season.
For the Numberplate, you do not put a number there, but your Nations 3-letter code, e.g FIN, LIT etc, in black.

Additionally : Thanks andro. for the Rescue car.
And, for those who does not own Photoshop, check third post below.

can you post it in a format combatible with old programs? BMP maybe

Attached in PNG, and font.