There was a special tool for installing them. It was just a drift with the correct tip. Upon hitting the "dome" in the middle of the rivet, the inside edge of rivet sort-of mushroomed behind/around the opening. Very simple and clever - and cannot be undone unless you drill them out (destroy them).
For those of you who like to BS "why", perhaps an attempt to make it just a little harder to swap ID plates (screws made swapping very easy)?
$8.95 for two one-purpose parts - try to make them, if you have time to waste.
