I don't care where you were a service manager, this:
The VIN is on that decal so you better have to prove ownership.
is incorrect.
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EDIT: Unless your statement is poorly worded.
It reads to me like you are saying that he needs to have that decal inorder to to prove ownership of the vehicle because it contains the VIN number. That is incorrect.
If you are saying that he better be able to prove ownership of the vehicle in order to obtain a new sticker, it's a different matter. I wouldn't argue with you on that one. If ford is the only place to get one and he wants an official reproduction, he's probably going to have to prove ownership like you say.
If it were mine, well... Being well out of warranty and not getting any work done at dealer, I wouldn't care about having the sticker or it being official. In fact since mine is going to be built into a custom truck I probably wouldn't want it to be official, but a creative forgery (with disclaimer somewhere) that had been subtly modified to reflect vehicle modifications. Ya know like color codes, tire sizes, axle tags, that sort of stuff. Something that only those in the know would notice.