[waterfowl]

even on trains? amtrak specifically questions people about cash?

This seems weird -- compared to traveling by air amtrak has approx 0 security, no TSA equivalent, bag scan, etc(unless you check maybe).

[r00fus]

They check cargo holds and do random bag checks - as of the mid 2000s due to the "war on terrah" but maybe that went out of fashion in the past decade. Large denomination bills are designed to be easily scanned externally since they contain metal strips in the bill design.