When a vehicle came down the line and a worker (line man, Q/A inspector, etc...) found or had a problem that couldn't be corrected, the car was was pulled off the line to be repaired. Before it could go back onto the line, it had to be "signed off" on that the vehicle again met the specifications. The document stayed with the car.
The line had to keep moving. That's why, for example, a seat would have only 3 out of four bolts installed.
Now, the norm on assembly lines is that any worker can stop the line if necessary to get the problem solved.
I found a wooden nickel good for a free car wash in Salt lake City. Never made it....