I came across some old legal docs the TSA filed, and found some interesting remarks in this one:

http://www.aclu.org/files/assets/TSA.Switzer_Decl_attachments_1_2_and_3_0.pdf

Page 19: “When currency appears to be indicative of criminal activity, TSA may report the matter to the appropriate authorities. For all flights, factors indicating that cash is related to criminal activity include the quantity, packaging, circumstances of discovery, or method by which the cash is carried, including concealment.” Continues to state that TSA will verify you’ve reported to CBP if >$10K is flying internationally.

Page 24: “When TSA discovers contraband during the screening process that is not a TSA Prohibited Item, the matter should be referred to the local Law Enforcement Officers as appropriate. An Enforcement Investigative Report should not be initiated. Examples of such contraband include: … Large amounts of cash ($10,000).”

The TSA is empowered by Congress ONLY to find weapons, explosives, and incendiaries. They often times report people for drug possession, arguing that they were searching for WEI but just “happened” to find drugs, and therefore it’s cool. But cash?! Cash isn’t illegal at all, and assuming malintent or trying to enforce customs rules is NOT within the scope of their mission.

Best part: they’re more likely to refer you to law enforcement if you conceal your cash. If you leave it in plain sight for the TSA to steal, it’s much more acceptable.