The USPS is the only carrier who insures numismatic
material over the maximums (low) of other carriers. See
my factual article (archived) where this information
was printed in both "Coin World" and "Numismatic
News." I include a bill of sale with insured items
which carry types PS Form 3813-P and PS Form 3813
(also with Registered mail) insurance. I suggested
over and over that persons visiting their local post
office pick up an insurance claim to study what is
expected of both buyer and seller.

JB