U.S. citizens who have an interest in, or signature authority over, a financial account are required to disclose the existence of such account on Schedule B, Part III of their individual income tax return. Additionally, U.S. citizens must file an FBAR with the U.S. Treasury disclosing any financial account in a foreign country with assets in excess of $10,000 in which they have a financial interest, or over which they have signatory or other authority. Those who willfully fail to file their FBARs on a timely basis, due on or before June 30 of the following year, can be assessed a penalty of up to 50 percent of the balance in the unreported bank account for each year they fail to file a required FBAR. (emphasis added -ss)
The neat part is they can assess more than you have over there.
Some other fun stories here.