According to 31 CFR 1022.320 [1], your bank is legally required to report on any transaction that it "knows, suspects, or has reason to suspect ... involves funds derived from illegal activity"

I don't know how the Treasury Department expects my bank to know if transactions involve funds derived from illegal activity, but damn is that creepy.

[1] http://www.law.cornell.edu/cfr/text/31/1022.320