First time I hear of such. Am quite puzzled.
The problem in Europe was to prove to have already bought a camera in land before leaving the country for a trip abroad, not to pay tax and VAT for it on return.
I got an Agfa Family (that S-8 camera with a grip to throw it away...) that got a certificate with ID data given at a local Antwerp customs office declaring its origin in Belgium and got at its grip a strip with a belgium customs seal as further proof. Looks really weird and I never came across such again.
The issue here was ostensibly not import duties, but trademark. The licensed importer owned the trademark in the US, and so the trademarked words like Nikon, or in the case above Asahi and Takumar, would be obliterated. Perhaps to prevent someone from importing the camera and then reselling it outside the licensed channel. I've always found it odd that US Customs bothered with this on individuals bringing back single items; I could understand if they would confiscate a container full of unlicensed imports, but grinding off one lens at a time seems like a waster of everyone's time. Later, unlicensed imports would happen on a bulk scale with the "gray market" imported products sold by big camera stores.
This is all long before my time, but I read about it, perhaps discussed on the Usenet photo newsgroups 25 years ago.
Back in the 80s I remember people talking about the issue you describe of needing to prove you had bought the camera before the trip, but by then I think it was already a non-issue in the US for amateurs. Maybe if you had expensive equipment it would matter. In the 90s I used to carry an expensive piece of scientific equipment in and out of the country, and got a letter from my university stating it had already been legitimately imported from the UK to US, but Customs never looked at it closely enough for me to need the letter.