engraving is to remove some material in a pattern. So if a make a picture from a piece of wood, by carving some shape in the front. Engraving is the process used to permanantly put names on the cases of electronic products. iphones have a service to engrave with your name before dispatch. . In a licence plate, it is not engraved, but actually coined, stamped, punched, forced to change shape, rather than removed. So all the material remains, the shapes of the letters are held still while the background is just pushed backward when not wanted to be in the front, in relief.

punched out probably means made with some sort of engraving machine----I guess capture car means a car they were going to use to capture or kidnap Eichmann------rig a system means to make a system, they needed some way to change license plates quickly-------tinker with means to work with or play with or try to design------contraption is a device or an invention ------trapdoor is something that opens in the floor to hide someone or something