I found that when exploring my new to me prius the other day. If yOu remove that cover it reveals the metal chasiss below. That particular spot has the vin engraved there. Good to know I guess if other vin labels have been tampered with.
I went to one of the plug-in day events today and I don't remember if it was a Nissan or a Honda, but it had the VIN# cover like that under the hood.
Some countries (such as China) require that number to be on there. Interstingly, if the number is damaged in any way during the manufacturing process, these countries will not allow the vehicle to be imported. They must be stamped to a very specific depth, such that they can not be ground off. You have to grind completely through the metal to remove the numbers.