Not just one at 10K: required reporting also for: more than 1 transactions at lower levels, which aggregated hit that figure-- or any single one just below that figure, especially when the number is rounded of instead of random-- say 8500 or 9000 instead of say 9238.67....
Plus... even worse, anything 2K & above that triggers suspicions. One of the guidelines is past/established pattern of activity: someone could be doing a slew of transactions, but that may be considered normal, so it wouldn't trigger any report, while conversely, you have an account sitting largely unused and/or with a min balance, then suddenly receive a couple of large wires / deposits(insert appropriate sinister tune here, LOL). Research/reference:
http://www.msb.gov/guidance/msb_supact.html
http://www.fincen.gov/index.html http://www.fatf-gafi.org/Members_en.htm
REQUIRED, not suggested-- for any bank, casino, insurance, credit, securities, commodities, etc., etc. Note: the regs cover just about anything-- examples: jewelry, gift certificates, stored value cards, etc.
Then there are sharing & reporting agreements at that 10K level with most countries too... of note, Mexico's threshold happens to be higher: 20K.
Here are three countries that absolutely refuse to monitor, much less share info-- to the point of irking certain US agencies: Nauru, Ukraine, Burma(Myanmar).