In the US people are not permitted to keep gold silver or cash in safety deposit boxes.
I don't believe that is true. It is true that the government confiscated gold under FDR, forcing people to take paper in exchange, but today it is legal to possess gold and silver. When currency, gold or silver again becomes illegal to possess (and that day will come), a government agent will be present when you open your safe deposit box.
Current FDIC remarks to the public discourage keeping cash in a safe deposit box (not insured, no interest), but at least for now, it is legal for the public to possess currency.