I'd never seen rivets used to secure a coin in a flip, but I went on the Italian e-bay to try and find some Vatican coins and there were quite a few on that site. Here's what it looks like
You see that very often for Italian (or Vatican) coins. It's the Italian counterpart of a slab. Coins in a flip secured by rivets are certified by the company written on the rivets.
Common in italy, its a bit comparable to the grading companies, like this numismatic shops certify a grade and authenticity of a coin.
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From the link you post I could see that the rivets has part of the name of the seller so rivets are customized... its not like everyone is using "ACME" rivets around.