Convoy plates

[Mrs Vampire]

OK
I want to know what is the official name for the plates that fit into the plate holder on the front and rear of most soft skinned vehicles.

I have forever called the things they fit into convoy plate holders and the plates that go in convoy plates .

I did a Google search looking for pictures of them and it seems no one calls them convoy plates.

I need the correct nomenclature and a link to a place where I can get info on them . I am especially after info on the markings on my tank which I am told are Mud and Blud .