F.V.
Yes, some of the bonds you mention have dipped into negative rates on the open markets, but were they sold with an initial coupon rate that was really negative? I hadn't read that. Either way, the initial coupon rates are set at the initial auction by the market, then they float on the secondary market based on what others are willing to pay. In neither case are those rates are set by the Fed or Central Banks, which is what the the original post was questioning.
+1 for nereo. I hadn't thought about strictly the infrastructure costs. Having been fortunate enough to have toured the Federal Reserve facility in Los Angeles, that's got to be a annual huge budget.