Identification possible german truck license plate

[gregory85]

Hello eveybody,
I found this license plate:

Photo 1 (Front): https://imgur.com/a/g1plK. It is about 32cm in lenght.
Photo 2 (Behind): https://imgur.com/a/ishzN. I am sorry for the photo out of focus.

Could someone help me understand something more? Is it a Wehrmacht license plate of a truck or what ? Unfortunately even if something were written it is illegible, completely rusty.

The last question but not the least why does have it a lock?

Thanks !