This rectangular "Silver plate" does indeed typically have the VIN as well as numerical trim and colour codes, and sometimes date of manufacture.
Often times the "Silver plate" is riveted to the firewall, although it can also be located on the drivers door jam or pretty much anywhere under the hood.
The "firewall" is the body panel behind the motor that forms a barrier between the front of the passenger compartment and the the back of the engine compartment (on a front mounted engine).
At any rate, in addition to the "silver panel", the VIN is typically stamped on the firewall itself. the Silver plate can easily be "doctored" by drilling out the pop-rivets, removing the original "silver plate" and then substituting either a "forged" silver plate or a silver plate removed from another donor car.
Doctoring the VIN that is stamped into the firewall is difficult to perform.